Influence of germination time on the morphological, structural, vibrational, thermal and pasting properties of potato starch from Solanum tuberosum Phureja group

doi:10.21203/rs.3.rs-3938446/v1

Download PDF

Research Article

Influence of germination time on the morphological, structural, vibrational, thermal and pasting properties of potato starch from Solanum tuberosum Phureja group

https://doi.org/10.21203/rs.3.rs-3938446/v1

This work is licensed under a CC BY 4.0 License

Journal Publication

published 31 Aug, 2024

Read the published version in Potato Research →

You are reading this latest preprint version

This work focuses on the study of the physico-chemical changes that take place during a short germination period in flours and starches of Creole potato. To this end, the changes in the composition of the flours and the structural, thermal, vibrational, functional and pasting changes of the germinated starches were evaluated during the 12-day germination period, which was measured every 4 days. The water absorption index (WAI) and swelling powder showed no significant changes. Germination resulted in a decrease in fat and ash content, but an increase in protein and amylose content. Scanning electron microscopy (SEM) showed no changes in the morphology of the starch during germination. X-ray diffraction showed that this starch contains nanocrystals with hexagonal crystal structure, which are not affected by germination. Differential scanning calorimetry (DSC) shows a shift of the gelatinization peak to the right, which could be attributed to the concentration effect. The pasting profiles of the isolated starches show no significant changes, indicating that the potato endosperm does not undergo any changes during germination and the final viscosity behaves like a hydrogel.

Creole potato

germination

starch

physicochemical properties

vibrational analysis

structural analysis

The potato, one of the “six healthy foods” recognized by the Food and Agriculture Organization of the United Nations (FAO), is grown in more than 150 countries around the world. Tetraploid potatoes are the most widely grown worldwide, but there is interesting potential for the widespread use of diploid genotypes. The "creole potato" is known for its round tubers with yellow flesh and skin and excellent organoleptic properties. The genotypes of the creole potato belong to the cultivated Solanum tuberosum Phureja group, which consists mainly of diploid potatoes, that have their center of diversity in the southern Andean region of Colombia and northern Ecuador (Duarte-Delgado et al. 2021).

During its formation, the potato tuber accumulates starch, reserve proteins and other metabolic products and behaves like a sink organ. At the end, the tuber enters the dormant phase, in which all sprouting is completely inhibited. Depending on the variety and environmental conditions, after a few days to a few months the tubers switch from the sink to the source state, mobilize their reserves and supply energy and substrates to the growing shoots.

During storage before tuber formation, the first phase of plant development begins in a soilless environment at 10–15°C and 80–85% relative humidity (RH). The metabolic processes characteristic of dormant tubers disappears and the changes leading to shoot development are intensified (Agrimonti et al. 2007; Grzesik et al. 2022).

Tubers contain starch as the most abundant nutrient and are considered an interesting source of other nutrients such as high-quality proteins, bioactive compounds such as dietary fiber, phenolic compounds, carotenoids, and vitamin C. However, these contents strongly depend on the gene and are highly dependent on the genotype and agroclimatic conditions (Thomas et al. 2021).

The germination of grains for a limited period of time leads to an increase in the activity of their hydrolytic enzymes, which break down important compounds such as starch, fiber and proteins. At the same time, sprouting of legumes has been used to alter the structure of macronutrients, improve digestibility by forming new compounds with higher bioactivity, soften the pungent taste and increase nutritional value, making them a potential ingredient for functional foods. Previous studies have shown that sprouting treatment effectively changes the physicochemical properties of starch from various seeds, significantly increases the foaming capacity and reduces the size of starch molecules which could be used to improve bread quality, and has the potential to promote the application of starch films in the packaging industry by increasing the elongation of the film (Li et al. 2017; Xu et al. 2019; Contreras-Jiménez et al. 2018; Xing et al. 2021; Rodriguez-Garcia et al. 2021; Lucas-Aguirre et al. 2023a; b).

Recently, sprouted grains have become the focus of interest as their nutritional quality has been improved by enzymatic effects. Starch is the most common carbohydrate in the human diet and is produced in most green plants as an energy store. Starch consists of linear and helical amylose and branched amylopectin, formed by the α-condensation of D-glucose units, where the amylose-amylopectin ratio varies depending on the botanical source, which affects the physicochemical properties of starch (Li et al. 2017; Xu et al. 2019; Contreras-Jiménez et al. 2018; Xing et al. 2021; Rodriguez-Garcia et al. 2021; Lucas-Aguirre et al. 2023a; b).

Esquivel-Fajardo et al. (2022) defined starch as micro- or submicron particles composed of different molecules, including two amylose and amylopectin molecules, fat, proteins, minerals, salts, and others, but they included in this definition that starch is also composed of nanocrystals with two different crystal structures. They reported the presence of nanocrystals with orthorhombic crystal structure, which indicate that this starch can be called A-type. Starches in which nanocrystals with hexagonal crystal structure are present are referred to as B-type, and starches in which nanocrystals with hexagonal and orthorhombic crystal structure are present are referred to as C-type. However, A-type, B-type and C-type are not a polymorphism as described in several papers on starch. This new definition means that it is very important to define the effects of germination of these starch components as a function of germination time. So far, there is still much to be done regarding the physicochemical changes during germination. The presence of nanocrystals in different starches was demonstrated by Gong et al. (2016) using the acid isolation method and transmission electron microscopy (TEM). However, the identification of crystalline phases was not reported. Rodriguez-Garcia et al. (2021) proposed a powder diffraction file to identify both crystal structures. Concerning to the crystal identification of the X-ray patterns of potato, Velásquez-Herrera et al. (2017), Dündar et al. (2009), and Lee (2015), indicated that it has a B-type shape, however, this is the classification for starches containing nanocrystals with hexagonal crystal structure. Caceres et al. (2012) reported that the amylose content generally below 20%. The results of thermal analysis, show that the onset (T_o) and peak (T_p) temperatures were between 59.1–63.5 and 62.6-67.88°C, respectively. The changes in gelatinization enthalpy were all around 21 J g^− 1.

Potato starch is considered to have nanocrystals with hexagonal crystal structure, and this bellows to the so-called B-type starches (Velásquez-Herrera et al. 2017). There is little information on the properties of native starch and the changes it undergoes during the sprouting process in the Solanum tuberosum Phureja group potato.

The aim of this work was to evaluate the effect of germination on the proximate composition of flours and on the morphological, structural, vibrational, thermal, and pasting properties of starches from the Solanum tuberosum Phureja group and to study the effects on their properties, in order to search for processing alternatives, especially in the development of fermented beverages.

2.1. Sample obtention

The potato variety Corpoica-Sol Andina was used in this study. First, a manual selection was carried out to exclude contamination and/or potatoes with phytosanitary problems. They were washed and disinfected for 5 minutes with a sodium hypochlorite solution at a concentration of 50 ppm to avoid problems with fungal infections during the germination process. The potatoes were then dried at 30°C with hot air. For each day of the germination process analysis (0, 4, 8, 12 days), 250 g were weighed and stored in the dark at room temperature (20°C) during the entire period to promote the germination process and observed as shown in Fig. 1. At the end of each germination period, flour and starch were immediately extracted as described below.

To obtain the sprouted flours, the sprouted potatoes were sliced at the end of each process and dried in a forced-air oven at 40°C for 48 hours. They were ground and the flours were sieved through a 100 sieve and then packed in zip-lock bags under controlled conditions of temperature and relative humidity until remaining tests were carried out.

2.2. Germination rate

Sprouting of potatoes was defined as a bud ≥ 2 mm. The germination percentage was calculated according to Eq. 1.

$$GR \left(\%\right)=\frac{{N}_{d}}{N} x 100\%$$

Where N_d indicates the number of germinated eyes, and N is the total number of eyes that could germinate (Yang et al. 2023).

2.3. Proximal analysis of germinated flours

For the proximate analysis of the Creole potato flours without germination (day 0) and with germination times of 4, 8 and 12 days, they were evaluated using the methods given by the AOAC (2006), where the moisture content (925.10) was determined by the gravimetric method in an oven at 105°C, until reaching constant weight; the fat (920. 39) was determined by solid-liquid extraction (Soxhlet method); fiber (978.10) was determined by digestion with sulfuric acid and sodium hydroxide solutions and calcination of the residue; ash (942.05) was determined by calcination to constant weight; and protein (920.15) was determined by quantifying the total nitrogen content in the sample (Kjeldahl), with a factor of 6.25.

2.4. Starch isolation

Starch was isolated from potatoes at 0, 4, 8 and 12 days of germination using the method proposed by Gutiérrez-Cortez et al. (2021); Rojas-Molina et al 2024. In brief, 100 g of peeled potatoes were cut into cubes of 1 cm edge length and liquefied with 400 ml of distilled water for 3 minutes. To separate the starch, they were passed through a 100-mesh sieve, the starch was decanted at 4°C for 12 hours, the supernatant was removed and to purify the starch, it was mixed with distilled water and then centrifuged at 2000 rpm to obtain isolated starch from each fraction. Subsequently, each fraction was dried in an oven at 40°C for 48 hours.

2.5. Starch content

The starch content of Creole potato flours with different germination times was quantified by polarimetric method, following the methodology proposed by Gasiński & Kawa-Rygielska (2022).

2.6. Amylose content

The amylose content in ungerminated (day 0) and germinated isolated potato starch at days 4, 8 and 12 was determined using the spectrophotometric method (620 nm) on the basis of the formation of the iodine-amylose complex formed by reacting dispersed and gelatinized starch granules quantified against a solution of known amylose concentration, after adjustment of a standard curve (Juliano et al. 1981).

2.7. Scanning electronic microscopy (SEM) of potato starch during germination

SEM images of isolated Creole potato starch and isolated starch for each day of germination worked were studied in a scanning electron microscope (JEOL, JSM-6060LV-Japan) with HV mode resolution. The samples were coated with gold and fixed in a sample holder with carbon tape. The electron accelerating voltage was 20 kV at a pressure of 12–20 Pa (Quintero-Castaño et al. 2020) (Quintero-Castaño et al. 2020).

2.8. Particle size distribution

The mean particle size distribution of germinated and ungerminated Creole potato starch particles (4, 8 and 12 days) was determined according to Mie's theory, using a refractive index of 1.52, the equipment used was a Mastersizer 3000 (Malvern Instrument Ltd., Worcestershire, UK), dispersing the starch particles in 0.5 L of water, up to a darkening level of 10 ± 1%, quantifying the D10, D50 and D90 percentiles (Lucas-Aguirre et al. 2019).

2.9. X-ray diffraction analysis

To obtain the X-ray diffraction patterns, powder samples of ungerminated and germinated (4, 8 and 12 days) creole potato starches were taken and packed in an aluminum pan. A high-resolution diffractometer (Rigaku-Ultima 4-USA) was used to obtain the X-ray diffraction patterns. The measurements were taken at an angle of 5 to 35° on a scale of 2θ, with a _CuKα radiation wavelength of λ = 0.1540 nm, at 35 kV and 15 mA (Quintero-Castaño et al. 2020).

2.10. Thermal properties of starch

To measure the temperatures T₀, T_p, T_e and enthalpy of gelatinization of isolated ungerminated and germinated (4, 8, and 12 days) Creole potato starches, samples (2.0 ± 0.1 mg) were hydrated with deionized water to 85% moisture (w/w), the heating profile was carried out from 30 to 120°C, at a heating rate of 5.0°C/min, using a previously calibrated DSC (Mettler Toledo, Greifensee, Switzerland) (Contreras-Jiménez et al. 2019).

2.11. Vibrational analysis

The vibrational analysis of starches isolated from ungerminated and germinated Creole potatoes at 0, 4, 8 and 12 days were characterized using an FTIR spectrophotometer (Perkin Elmer, Spectrum Two-USA) using attenuated total reflectance, recording the transmittance between 600 and 4000 cm^− 1 (Contreras-Jiménez et al. 2019).

2.12. Pasting properties

The apparent viscosity profiles of the isolated ungerminated and germinated starches at different times (0, 4, 8 and 12 days) were determined using a modular compact rheometer (Anton Paar MCR 102- UK), a constant frequency of 193 rpm was used, the samples were heated in 5.3 min, from 50 to 92°C, then held for 1 min and then cooled at the same rate to the initial temperature and held for 1 min (Rincón-Londoño et al. 2016).

2.13. Functional properties of starches

A 2% (w/v) starch suspension was prepared, stirred and placed in a water bath at 90°C for 30 minutes, then cooled and centrifuged at 2000 rpm for 20 minutes, the supernatant was removed and placed in an oven at 105°C until constant weight was obtained, the respective weights were taken including the weight of the sediment and calculations were performed, determining the swelling power (SP), water solubility index (WSI) and water absorption index (WAI) (Contreras-Jiménez et al. 2019).

2.14. Statistical analysis

The tests were performed in triplicate, applying an analysis of variance with a significance level of 5% and Tukey's test, for the comparison of means using Statgraphics Centurion XVIII software.

3.1. Germination rate

When dormancy is broken, germination begins. Germination is the most important visible milestone for determining the physiological age of the tuber. The first observable stage of germination is characterized by the appearance of small white buds, often referred to as "pipping" or "peeping" (Mani et al. 2014). As shown in Fig. 1e, which corresponds to day 4 of the germination process, 37.8 ± 2.45% of the eyes have germinated, increasing to 72.64 ± 4.38% on day 6 (Fig. 1i) and 98.62 ± 2.28% (Fig. 1m) on day 12 of the germination process. These results are in agreement with those of Yang et al. (2023), who worked with the potato variety Solanum tuberosum 'Xisen no. 6' (Shepody × XS9304). Finally, as apical dominance decreases, multiple sprouting gradually develops, characterized by the appearance of multiple buds sprouting along the tuber, with both the duration of apical dominance and the number of sprouts per tuber being a varietal trait (Mani et al. 2014).

3.2. Proximate analysis of flours

Potatoes tend to be irregular in shape and size after harvest. Potato sprouting is a complex process involving several metabolic pathways as well as physiological and biochemical changes. Enzymatic reactions, carbohydrate metabolism and hormonal regulation are linked to the sprouting of potato tubers. Among the most important changes, the activity of enzymes related to sprouting gradually increases before sprouting, especially amylase activity, which rapidly increases during bud growth, and hydrolyzes starch to produce a large amount of sugar and energy for bud growth (Neupane et al. 2022; Yang et al. 2023). At the same time, some changes occur, such as the loss of weight, texture, nutritional value, softening, shrinkage and the formation of toxic alkaloids. Thus, in general, an average weight loss of 3.16 ± 1.00% was observed in each of the studied potatoes during the 12 days of germination, as well as softening, shrinkage and wilting of weight loss. Tuber weight loss during germination occurs through the periderm, and to a lesser extent through the lenticels (Mani et al. 2014).

Table 1 shows the changes in the composition of Creole potato flour during germination process and shows statistically significant differences in the individual components as germination progresses (p < 0.05). The most important changes include the decrease in fat (-70.56%), fiber (-19.26%) and ash (-49.48%) and the increase in protein (+ 21.8%).

Table 1

Proximate composition of flours creole potato at different days of germination.
Time (days)	Fat (%)	Fibre (%)	Ash (%)	Protein (%)	Starch (%)	Moisture (%)	Amylose (%)
0	1.80 ± 0.11^c	3.79 ± 0.14^b	1.94 ± 0.11^b	3.67 ± 0.09^ab	77.32 ± 1.34^a	8.48 ± 0.17^c	22.96 ± 0.74^a
4	0.72 ± 0.04^b	3.11 ± 0.15^a	1.80 ± 0.14^b	3.57 ± 0.08^a	79.63 ± 2.03^b	7.97 ± 0.05^b	24.76 ± 1.2^ab
8	0.69 ± 0.02^b	3.20 ± 0.20^a	0.96 ± 0.06^a	4,37 ± 0.33^ab	80.97 ± 1.84^b	6.81 ± 0.09^a	27.56 ± 1.08^c
12	0.53 ± 0.01^a	3.06 ± 0.20^a	0.98 ± 0.02^a	4.47 ± 0.88^b	79.15 ± 0.95^b	8.81 ± 0.22^d	31.43 ± 0.94^d

Data are expressed as mean ± standard deviation (SD) from three replicates. Different letter in columns indicate significant differences (p < 0.05) by Tukey’s test.

During germination, the sprouts begin to grow after awakening from dormancy and form roots at their base. At this point, the tubers change from a storage organ to a source of nutrients and energy for the developing sprouts. The fat content decreases, which could be due to the fat being used as an energy source during the respiration process (Table 1), which is triggered when the tuber awakens from dormancy during post-harvest storage (Neupane et al. 2022). The same behavior has been observed during germination of legumes such as lentils and peas (Lucas et al. 2023a, b).

Tuber dormancy is controlled by phytohormones, which play an important role in triggering or inhibiting tuber dormancy in potatoes. All five major plant hormones are involved in this process: Abscisic acid and ethylene are involved in triggering dormancy, cytokinins are involved in breaking dormancy, and gibberellins and auxins are involved in sprout development. When potato dormancy is broken, the cellular balance is disturbed and a cascade of biochemical reactions is triggered, which include the migration of calcium ions into the meristems, increased cellular respiration, and increased production of adenosine triphosphate (ATP), which could explain the decrease in minerals during the germination process (Table 1). These responses could explain the appearance of apical and proximal buds and the decrease in membrane integrity in the bulb during germination. These results indicate that moderate oxygenation of cells by hydrogen peroxide leads to an increase in intracellular Ca²⁺, iron concentration and active entry into mitosis, triggering germination, while at the same time the presence of hydrogen peroxide during germination acts on tuber protein metabolism. Indeed, germination is accompanied by protein carbonylation of the reserves, which makes them more sensitive to proteases and proteolysis, as well as a decrease in the activity of the pentose phosphate pathway. This explains the depolymerization of starch to reducing sugars (glucose and fructose) in the potato tuber at the end of dormancy (Zabrouskov et al. 2002; Delaplace et al. 2008; Mani et al. 2014).

The starch content found in the flours of the potato variety Corpoica - Sol andina, varied between 77.32–80.97% (Table 1), results higher than those obtained by Zarate-Polanco (2014), who worked with 17 promising clones, whose results varied between 45.23–72.98%, although the proximate composition of the flours may depend on the type of tuber, cultivation practices, climate, soil type and presence of pests and diseases, among others factors.

The results for percentage amylose content (Table 1) generally showed a similar behavior to those reported by Cáceres et al. (2012), with starches from 24 diploid potato accessions of the Phureja group (19.7–25.8%) and of 2 commercial tetraploid potato cultivars of the Solanum tuberosum group (24-24.8%). It could be analyzed that the Phureja starch has a lower ratio between short/ long chains than the S. tuberosum starch, i.e. a higher proportion of long chains characteristic of amylopectin, which may have a major impact on the functional properties of the starch. At the same time, it is observed that the amylose content increases with increasing germination time, which is partly due to the conversion of amylopectin chains into amylose (Mueez-Ali et al. 2023).

Pineda-Gómez et al. (2021) reported amylose content between 29 and 40% for starch from six potato varieties (Solanum tuberosum) grown in the Andean region of southern Colombia and Mueez-Ali et al. (2023) found amylose contents of native potato starches in the range 25.71–26.60%.

3.3. Morphological changes in isolated potato starch during the germination process

Figure 2a and 2b shows the morphological differences that occur in the starch grains of creole potatoes. The small grains have a round shape and are on average 181.88 ± 28.13 µm long at their longest point, while the larger ones have an ovoid and/or elliptical shape and are on average 375.08 ± 87.45 µm long at their longest point. In general, the starch granules a have smooth, homogeneous, and slightly uneven surface. At the same time, smaller circular round particles corresponding to protein molecules with an average diameter of 38.69 ± 11.11 µm can be seen on the SEM images.

The same behavior was reported by Choi et al. (2020) in potato starch (Solanum tuberosum L.), in which where all samples showed a similar morphology, round, oval or elliptical, with a mixture of large, medium and small starch granule, and a shiny surface with a regular pattern. Small granules were mostly spherical, while large granules have an ellipsoidal in shape (Cáceres et al. 2012).

When analyzing the possible effects of the germination process through the enzymatic activity on the integrity of the Creole potato starch granules (Fig. 2c-h), their surface changed throughout the process, this fact indicates that during the germination process, which leads to the development of stems and roots, fats, and proteins, the starch granules are not altered.

The most representative change in the starch granules during the germination process, initially was the increase in the average diameter of the starch granules of Creole potato in the D90 percentile, manifesting as superficial and spongy erosion of the granules and formation of superficial pores in them, these changes could be associated to the enzymatic hydrolysis that penetrates the interior of the granules from the heliotic region towards the exterior; while in the D10 and D50 percentiles the average diameter of the granules decreased (Lucas-Aguirre et al. 2023b).

Cáceres et al. (2012) reported that size of the starch granules ranged from 0.5 to 120 mm in 24 diploid accessions of the Phureja group, where the proportion of small granules (0.4–10 mm) being 10% v/v for the Phureja group and almost 6% in S. tuberosum starches. In addition, the mean particle size (D50) of the starch extracted from Phureja was smaller (less than 30.2 mm) than that of S. tuberosum (34.5–41.2 mm).

3.4. Functional properties of isolated potato starch during germination

In general, the germinated starch of Creole potato was found to have high WAI (g gel/g sample) (11.86 ± 0.52–10.43 ± 0.11) and SP (%) (12.07 ± 0.55–10.61 ± 0.10) and low values for WSI (%) (2.58 ± 0.21–1.79 ± 0.15) (Table 2), indicating that it is a good quality starch. The WAI decreased by 12.06% as the germination time progressed; while the SP decreased by 12.1%, which is consistent with the results of the RVA tests (Fig. 5), where the peak viscosity decreases with increasing germination time. This could be due to the hydroxylation of amylose and amylopectin, which leads to a decrease in peak and final viscosity and causes the paste to behave like a hydrogel.

It is known that starch can reversibly absorb water before heating, but when the temperature raises close to the gelatinization temperature, water absorption is irreversible. This property indicates the ability of the granules to swell and quickly reach the viscosity peak, while the WAI measures the swelling capacity which depends on the availability of hydrophilic groups and the ability of the macromolecule to form a gel. On the other hand, the WSI is related to the number of soluble solids and the WAI is mainly related to the damage of the starch and the presence of compounds other than starch, e.g. minerals (Pineda-Gómez et al. 2021).

Table 2

Functional properties and Particle size distribution of germinated creole potato starch at different days of germination.
Time (days)	WAI g (g gel/g sample)	WSI (%)	SP (%)	D10 (µm)	D50 (µm)	D90 (µm)
0	11.86 ± 0.52^b	2.46 ± 0.11^bc	12.07 ± 0.55^b	22.47 ± 2.68^b	25.68 ± 8.18^a	45.71 ± 5.99^a
4	10.83 ± 0.17^a	2.29 ± 0.11^b	11.00 ± 0.17^a	22.57 ± 2.78^b	35.67 ± 3.35^b	59.33 ± 5.31^b
8	11.07 ± 0.94^ab	1.79 ± 0.15^a	11.21 ± 0.96^ab	20.67 ± 0.75^ab	38.33 ± 9.85^b	69.00 ± 4.38^c
12	10.43 ± 0.11^a	2.58 ± 0.21^c	10.61 ± 0.10^a	18.12 ± 0.33^a	40.33 ± 9.21^bc	70.22 ± 7.34^c

Data are expressed as mean ± standard deviation (SD) from three replicates. Different letter in columns indicate significant differences (p < 0.05) by Tukey’s test.

Pineda-Gómez et al. (2021) reported very low WAI and WSI values in 6 potato starches of the genus Solanum tuberosum, where WAI values ranged from 1.95 to 2.39 g/g, while WSI ranged from 0.31 to 1.28%, relatively low values compared to the starches of the Phureja group, where they found that the apparent swelling of starch granules is a property mainly attributed to amylopectin. However, the mineral content in the starch may contribute to the water absorption capacity and therefore affect other physical properties such as viscosity development. The low solubility at low temperatures could be attributed to the crystalline structure of starch and the presence of hydrogen bonds between -OH groups within the starch molecules. In addition, the solubility index tends to increase when the gelatinization temperature of the starch is exceeded.

3.5. Structural characterization

Figure 3 shows the X-ray diffraction patterns of isolated starch from Creole potato during the germination period. Rodriguez-García et al. (2021) have indexed the patterns for nanocrystals with hexagonal crystal structure. The dashed line in these patterns corresponds to the identification of this structure.

This means that this starch can be classified as B-type (Velasquez-Herrera et al. 2017). As can be observed, germination does not cause any significant change in the crystalline structure of these starch grains, which means that the enzymatic process does not affect the nanocrystals with hexagonal crystal structure. It is possible that during germination the potato uses only the hydrolyzed amylose and amylopectin or part of the fat and proteins as the main energy source and that under the conditions of germination the plant does not need the more packed energy reservoir in the hexagonal crystals.

On the other hand, it is important to note that these X-ray patterns show broad peaks related to the presence of nanocrystals that generate elastic and inelastic scattering simultaneously (Londoño-Restrepo et al. 2018). The behavior of nanocrystals along the germination time is still an open problem, because in this case the potato was germinated under dark conditions. However, in the case, where the Creole potato is planted a few centimeters deep. The use of all energy sources contained in the starch is limited by the beginning of the photosynthetic process in the leaves, which produce starch in the plant and prevent the use of the reserves (nanocrystals) contained in the mother seeds.

Using Table 3, and with the help of the reports of Rodriguez-Garcia et al. (2021), it is possible to identify each of the diffraction peaks allowed for hexagonal crystal structure.

Table 3

Miller indexes, Bragg angles, and interplanar spacing for the hexagonal crystal structure in creole potato starch.
hkl	This work (2θ)	Reported*
hkl	This work (2θ)	Hexagonal (2θ)
(100)	5.6270	5.5056
(200)	11.4581	11.0240
(201)	14.2043	13.8500
(120)	14.9567	14.6003
(211)	17.1261	16.8462
(112)	19.5839	19.3220
(400)	22.1797	22.1516
(230)	24.0105	24.1679
(132)	26.1924	26.1631
(322)	29.8792	29.5572
(510)	31.2335	31.0195
(104)	34.2305	34.3669
(342)	38.0426	38.1101

*Rodriguez-Garcia et al. (2021).

3.6. Vibrational analysis

Figure 4 shows the IR spectra obtained from the isolated starches during the germination process. The main components of the starch do not change and the formation of new compounds because of the starch germination process is not observed, which could be related to the lack of proteins and fats in the starch.

In general, the absorption band in the region around 3350 cm^− 1 in starches corresponds to the symmetric and asymmetric stretching of intra- and intermolecular hydroxyl groups. The band observed around 2900 cm^− 1 is related to the stretching of C-H bonds. During germination, changes occur in the starch granules, which are triggered by the enzymatic process. This creates sugar chains that are used by the grain as a source of carbon and energy for growth (Contreras et al. 2018). Figure 4 shows changes in the vibrational spectrum of starch between 1700 and 1200 cm^− 1, with the 1643 cm^− 1 band corresponding to the carbonyl groups (Mueez-Ali et al. 2023). In the range between 1350 and 1275 cm^− 1 weakening is observed in the bands corresponding to the carbonyl group, possibly due to changes in the α (1–4) and α (1–6) glycosidic linkage. Similar results were reported by Daneri et al. (2016); Contreras et al. (2019) in malted barley, showing that significant changes occur in the starch granules during malting. The main changes in these starches during germination are in the bands between 3280–3350 cm^− 1 and between 980–1040 cm^− 1 corresponding to the 0-H bonds and the anhydrous glucose ring, respectively, increasing the intensity of the peaks (Fig. 4).

3.7. Thermal analysis

Gelatinization is perhaps the most important property to consider when processing starch. It is a transition from order-to disorder in the internal structure of the grains and is very sensitive to the presence of plasticizers such as water. Esquivel-Fajardo et al. 2024, indicate that this transition can be in part caused by the solvation of the nanocrystals with hexagonal or orthorhombic crystal structures. The transition temperatures and enthalpy change due to the changes in these nanocrystals. The temperature at the peak (T_p) in some cases be regarded as the point at which gelatinization is complete. The energy required for gelatinization can be measured by enthalpy (ΔH) and is indicated by the area under the curve in the DSC thermogram and is also an indicator of the molecular changes within the granules that occur during gelatinization (Pineda-Gómez et al. 2021).

Figure 5 shows the DSC results of the germinated starch of creole potato, where a slight increase in T_p is observed with increasing germination time, which remainis constant from 62.2°C on day 0 of germination to day 4 and increases to 63.2°C after 8 days of germination until reaches a T_p of 63.8°C after 12 days of germination, which could be attributed to the accumulation of sugars during germination. After 12 days of germination a T_p of 8°C was observed, which could be attributed to the accumulation of sugars during germination. This discrepancy in gelatinization temperature after germination could be attributed to differences in germination conditions and plant sources (Wu et al. 2013), while enthalpy showed the same behavior, increasing with increasing starch germination time but requiring less energy, to achieve gelatinization of starch granules at day 12 (Fig. 5). This behavior could be due to weakly associated double helices in non-crystalline regions, while the decrease in gelatinization enthalpy could be due to the lower proportion of longer branched chains that could form a shorter double helix order, leading to a decrease in gelatinization enthalpy (Wu et al. 2013).

These values determined for T_p were comparable with those of other studies, while the gelatinization enthalpies differed significantly. In Cáceres et al. (2012), working with twenty-four diploid accessions of the Phureja Group, The T_p values ranged between 62.6 and 67.88°C and the changes in gelatinization enthalpy varied very little in a range between 19.4 and 22.0 J g^− 1. At the same time, he reports that he found no significant differences between the thermal properties of Phureja and S. tuberosum starches. Granule crystallinity increases with amylopectin, and the enthalpy of gelatinization (△H) from DSC analysis gives a general quantitative and qualitative measure of crystallinity, which is an indicator of the loss of molecular order within the grains.

Choi et al. (2020) and Pineda-Gómez et al. (2021) report T_p (peak) values between 60.29–63.80°C and gelatinization enthalpy changes (△H) in the range between 7.95 and 8.88 J g^− 1, for starches of the genus tuberosum, as found in this study.

3.8. Pasting properties

One of the main reasons for grain seed germination kernel seeds is to reduce the peak and end viscosity of the slurry to convert the original unmalted grain into a slurry with low end viscosity, which is formed by the hydroxylation of amylose and amylopectin, and to utilize the hexagonal nanocrystals in free D-glucose units that can ferment and produce alcohol. Grains such as corn, amaranth and sorgum have a high end viscosity, but the enzymatic process leads to the hydroxylation of amylose and amylopectin, decreasing the peak and end viscosity and making the slurry behave like a hydrogel (Pineda-Gómez et al. 2021).

Figure 6 shows the pasting profiles of starches, and it is important to recognize two points in these curves that serve to compare the differences between starches: (1) The peak viscosity, or the highest apparent viscosity reached, is the point at which the starch has lost its granular form and the leached amylose and amylopectin chains occupy more space and contribute to the increase in paste viscosity under heating conditions; (2) The final viscosity corresponds to the rearrangement of the chains during cooling and temperature reduction (Londoño-Restrepo et al. 2018).

Regarding the peak viscosity of the germinated starch of creole potato, it is observed that it develops high viscosity peaks that decrease with increasing germination time, suggesting that the long amylose and amylopectin chains are fractionated, leading to an increase in reducing sugars and a decrease in apparent viscosity, although no enzymatic attack on the integrity of the starches is observed (Oseguera-Toledo et al. 2020).

Due to their viscosity profile, these potato varieties have great potential to be used as thickeners in various food formulations. The increase in viscosity upon cooling indicates the ability of the starch to form gels by regrouping the leached granule chains. When the final viscosity is low, the starch-water dispersion behaves like a hydrogel, as in the case of starch from Creole potatoes (Fig. 6).

The SEM images show that the starch grainules do not suffer any external damage as a result of the enzymatic process. However, the peak and final viscosity decreases and the slurry behaves like a hydrogel. The starch nanocrystals are normaly dissolved by the heat and excess water in the slurry.

The study of the short-term germination of this potato has shown that the starch grains do not show any surface or morphological changes, which indicates that germination is not controlled by enzymatic processes in the first stages. This finding is confirmed by the fact that the functional properties of the isolated starch showed no significant changes. X-ray diffraction showed that the nanocrystals with hexagonal crystal structure do not undergo any changes during germination. This is an important indication, as these nanocrystals are the main source of energy storage. The gelatinization may be partly due to the solvation of the hexagonal crystals, but it is still an interesting phenomenon that requires further investigation.

Conflict of interest

The authors have no actual or potential conflict of interest that could inappropriately influence their research. The authors have conducted themselves within the bounds of ethical behaviors. This is an original work. However, work and the words of other authors have been cited according to the references. All authors have seen and approved the final version of the paper and consented to its publication.

Acknowledgments

The authors thank of the University of Quindío, especially the Vice Rector for Research, for funding the project called “Evaluación de la potencialidad de leguminosas y tubérculos en la producción de bebidas alcohólicas fermentadas libres de gluten”. This work was financially supported by the Laboratorio Nacional de Caracterizacion de Materiales CFATA-UNAM, (Conhacyt-Mexico) at Campus Juriquilla.

International AOAC (2006) Official methods of analysis of AOAC International, 20 edn. AOAC International, Rockville (USA)
Agrimonti C, Visioli G, Bianchi R, Torelli A, Marmiroli N (2007) G1-1 and LeG1-1/LeG1-2 genes are involved in meristem activation during breakage of dormancy and early germination in potato tubers and tomato seeds. Plant Sci 173:533–541. htts://doi:10.1016/j.plantsci.2007.08.004
Aguilar J, Miano AC, Obregón J, Soriano-Colchado J, Barraza-Jáuregui G (2020) Malting process as an alternative to obtain high nutritional quality quinoa flour. J Cereal Sci 90:102858. https://doi.org/10.1016/j.jcs.2019.102858
Cáceres M, Mestres C, Pons B, Gibert O, Amoros W, Salas E, Dufour D, Bonierbale M, Pallet D (2012) Physico-chemical characterization of starches extracted from potatoes of the group Phureja. Starch/Stärke 64:621–630. 10.1002/star.201100166 621
Choi I, Chun J, Choi HS, Park J, Kim NG, Lee SK, Park CH, Jeong KH, Nam JW, Cho J, Cho K (2020) Starch characteristics, sugars and thermal properties of processing potato (Solanum tuberosum L.) Cultivars Developed in Korea. Am J Potato Res 97:308–317. https://doi.org/10.1007/s12230-020-09779-z
Contreras-Jiménez B, Del Real A, Millán-Malo BM, Gaytán-Martínez M, Morales- Sánchez E, Rodríguez-García ME (2019) Physicochemical changes in barley starch during malting. J Inst Brew 125:10–17. https://doi.org/10.1002/jib.547
Delaplace P, Rojas-Beltran J, Frettinger P, du Jardin P, Fauconnier ML (2008) Oxylipin profile and antioxidant status of potato tubers during extended storage at room temperature. Plant Physiol Biochem 46:1077–1084
Duarte-Delgado D, Narváez-Cuenca CE, Restrepo-Sánchez LP, Kushalappa A, Mosquera-Vásquez T (2021) Development and validation of a liquid chromatographic method to quantify sucrose, glucose, and fructose in tubers of Solanum tuberosum Group Phureja. J Chromatogr B 975:18–23. http://dx.doi.org/10.1016/j.jchromb.2014.10.039
Dündar E, Yusuf T, Blaurock A (2009) Large scale structure of wheat, rice and potato starch revealed by ultra-small angle X-ray diffraction. Int J Biol Macromol 45(2):206–212. http://dx.doi.org/10.1016/j.ijbiomac.2009.05.002
Esquivel-Fajardo EA, Martínez-Ascencio EU, Oseguera-Toledo ME, Londoño-Restrepo SM, Rodríguez-García ME (2022) Influence of physicochemical changes of the avocado starch throughout its pasting profile: Combined extraction. Carbohydr Polym 281:119048. https://doi.org/10.1016/j.carbpol.2021.119048
Gasiński A, Kawa-Rygielska J (2022) Mashing quality and nutritional content of lentil and bean malts. LWT - Food Sci Technol 169:113927. https://doi.org/10.1016/j.lwt.2022.113927
Gong B, Liu W, Tan H, Yu D, Song Z, Lucia LA (2016) Understanding shape and morphology of unusual tubular starch nanocrystals. Carbohydr Polym 151:666–675. https://doi.org/10.1016/j.carbpol.2016.06.010
Grzesik M, Janas R, Steglińska A, Kręgiel D, Gutarowska B (2022) Influence of microclimatic conditions during year-long storage of ‘Impresja’ potato tubers (Solanum tuberosum L.) on the emergence, growth, physiological activity and yield of plants. J Stored Prod Res 99:102033. https://doi.org/10.1016/j.jspr.2022.102033
Gutiérrez-Cortez E, Hernández-Becerra E, Londoño-Restrepo SM, Rodríguez-García ME (2021) Physicochemical characterization of Amaranth starch insulated by mechanical separations. Int J Biol Macromol 177:430–436. https://doi.org/10.1016/j.ijbiomac.2021.02.138
Hernández-Becerra E, Contreras-Jiménez B, Vuelvas-Solorzano A, Millán-Malo B, Muñoz-Torres C, Oseguera-Toledo ME, Rodríguez-García ME (2020) Physicochemical and morphological changes of corn grains and starch during the malting for Palomero and Puma varieties. J Cereal Sci 97(2):404–415. https://doi.org/10.1002/cche.10256
Juliano BO, Perez CM, Blakeney AB, Castillo T, Kongseree N, Laignelet B, Lapis ET, Murty VVS, Paule CM, Webb BD (1981) International cooperative testing on the amylose content of milled rice. Starch-Stärke 33:157–162. https://doi.org/10.1002/star.19810330504
Lee JC, Tae-Wha M (2015) Structural characteristics of slowly digestible starch and resistant starch isolated from heat–moisture treated waxy potato starch. Carbohydr Polym 125:200–205. http://dx.doi.org/10.1016/j.carbpol.2015.02.035
Li C, Ohb SG, Lee DH, Baik HM, Chung HJ (2017) Effect of germination on the structures and physicochemical properties of starches from brown rice, oat, sorghum, and millet. Int J Biol Macromol 105:931–939. http://dx.doi.org/10.1016/j.ijbiomac.2017.07.123
Lucas-Aguirre JC, Giraldo-Giraldo GA, Cortés-Rodríguez M (2019) Stability during storage of coconut powder fortified with active components. Biotecnología En El Sect Agropecuario y Agroindustrial 17(2):66–76
Lucas-Aguirre JC, Quintero-Castaño VD, Castañeda-Cano LF, Rodríguez-García ME (2023a) Morphological, structural, chemical, vibrational, thermal, pasting, and functional changes in pea starch during germination process. F1000Research 12:940. https://doi.org/10.12688/f1000research.136568.1
Lucas-Aguirre JC, Quintero-Castaño VD, Rodríguez-García ME (2023b) Study of the changes on the physicochemical properties of isolated lentil starch during germination. Int J Biol Macromol
Londoño-Restrepo SM, Rincón-Londoño N, Contreras-Padilla M, Millán-Malo BM, Rodríguez-García ME (2018) Morphological, structural, thermal, compositional, vibrational, and pasting characterization of white, yellow, and purple Arracacha Lego-like starches and flours (Arracacia xanthorrhiza). Int J Biol Macromol 113:1188–1197. https://doi.org/10.1016/j.ijbiomac.2018.03.021
Mani F, Bettaieb T, Doudech N, Hannachi C (2014) Physiological mechanisms for potato dormancy release and sprouting: A review. Afr Crop Sci J 22(2):155–174
Mueez-Ali S, Siddique Y, Mehnaz S, Bilal-Sadiq M (2023) Extraction and characterization of starch from low-grade potatoes and formulation of gluten-free cookies containing modified potato starch. Heliyon 9:e19581. https://doi.org/10.1016/j.heliyon.2023.e19581
Neupane S, Sharma S, Sigdel S, Duwal R (2022) Effect of pre-sowing treatment of chemicals on sprouting of newly harvested potato at Kavre, Nepal. Int J Agricultural Appl Sci 3(2):108–113. https://doi.org/10.52804/ijaas2022.3220
Oseguera-Toledo ME, Contreras-Jiménez B, Hernández-Becerra E, Rodriguez-Garcia ME (2020) Physicochemical changes of starch during malting process of sorghum grain. J Cereal Sci 95:103069. https://doi.org/10.1016/j.jcs.2020.103069
Pineda-Gomez PP, Mutis-González N, Contreras-Jimenez B, Rodriguez-Garcia ME (2021) Physicochemical characterisation of starches from six potato cultivars native to the Colombian andean region. Potato Res 64:21–39. https://doi.org/10.1007/s11540-020-09462-0
Rincón-Londoño N, Vega-Rojas LJ, Contreras-Padilla M, Acosta-Osorio AA, Rodríguez-García ME (2016) Analysis of the pasting profile in corn starch: structural, morphological, and thermal transformations, Part I. Int J Biol Macromol 91:106–114. https://doi.org/10.1016/j.ijbiomac.2016.05.070
Rodríguez-García ME, Hernández-Landaverde MA, Delgado JM, Ramírez-Gutierrez CF, Ramírez-Cardona M, Millán-Malo BM, Londoño-Restrepo SM (2021) Crystalline structures of the main components of starch. Curr Opin Food Sci 37:107–111. https://doi.org/10.1016/j.cofs.2020.10.002
Thomas S, Vásquez-Benítez JD, Cúellar-Cepeda FA, Mosquera-Vásquez T, Narváez-Cuenca CE (2021) Vitamin C, protein, and dietary fiber contents as affected by genotype, agro-climatic conditions, and cooking method on tubers of Solanum tuberosum Group Phureja. Food Chem 349:129207. https://doi.org/10.1016/j.foodchem.2021.129207
Velásquez-Herrera JD, Lucas-Aguirre JC, Quintero-Castaño VD (2017) Physical-chemical characteristics determination of potato (Solanum phureja Juz. & Bukasov) starch. Acta Agronómica 66(3):323–330. https://doi.org/10.15446/acag.v66n3.52419
Wu F, Chen H, Yang N, Wang J, Duan X, Jin Z, Xu X (2013) Effect of germination time on physicochemical properties of brown rice flour and starch from different rice cultivars. J Cereal Sci 58:263–271. https://doi.org/10.1016/j.jcs.2013.06.008
Xing B, Teng C, Sun M, Zhang Q, Zhou B, Cui H (2021) Effect of germination treatment on the structural and physicochemical properties of quinoa starch. Food Hydrocolloids 115:106604. https://doi.org/10.1016/j.foodhyd.2021.106604
Xu M, Jin Z, Simsek S, Hall C, Rao J, Chen B (2019) Effect of germination on the chemical composition, thermal, pasting, and moisture sorption properties of flours from chickpea, lentil, and yellow pea. Food Chem 295:579–587. https://doi.org/10.1016/j.foodchem.2019.05.167
Yang X, An J, Wang X, Wang L, Song P, Huang J (2023) Ar plasma jet treatment delay sprouting and maintains quality of potato tubers (Solanum tuberosum L.) by enhancing antioxidant capacity. Food Bioscience 51:102145. https://doi.org/10.1016/j.fbio.2022.102145
Zabrouskov V, Kumar G, Sychalla J, Knowles N (2002) Oxidative metabolism and the physiological age of seed potatoes are affected by increased α-linolenate content. Physiol Plant 116:172–185. https://doi.org/10.1034/j.1399-3054.2002.1160206.x
Zarate-Polanco L (2014) Extracción y caracterización de almidón nativo de clones promisorios de papa criolla (Solanum tuberosum, Grupo Phureja). Revista Latinoam de la Papa 18(1):1–24

Download PDF

Journal Publication

published 31 Aug, 2024

Read the published version in Potato Research →

Reviewers agreed at journal
01 Jun, 2024
Reviewers invited by journal
24 Mar, 2024
Editor assigned by journal
24 Mar, 2024
First submitted to journal
21 Mar, 2024

You are reading this latest preprint version

Influence of germination time on the morphological, structural, vibrational, thermal and pasting properties of potato starch from Solanum tuberosum Phureja group

Status:

Journal Publication

Version 1

Abstract

Figures

1. Introduction

2. Materials and methods

2.1. Sample obtention

2.2. Germination rate

2.3. Proximal analysis of germinated flours

2.4. Starch isolation

2.5. Starch content

2.6. Amylose content

2.7. Scanning electronic microscopy (SEM) of potato starch during germination

2.8. Particle size distribution

2.9. X-ray diffraction analysis

2.10. Thermal properties of starch

2.11. Vibrational analysis

2.12. Pasting properties

2.13. Functional properties of starches

2.14. Statistical analysis

3. Results

3.1. Germination rate

3.2. Proximate analysis of flours

3.3. Morphological changes in isolated potato starch during the germination process

3.4. Functional properties of isolated potato starch during germination

3.5. Structural characterization

3.6. Vibrational analysis

3.7. Thermal analysis

3.8. Pasting properties

4. Conclusions

Declarations

Conflict of interest

Acknowledgments

References

Status:

Journal Publication

Version 1