This is the first study to examine the use of seaweed flour, especially from Gracilaria sp., as a substitute for tapioca flour in boba pearls. Several other investigations have been carried out using different seaweed species, namely Kappaphycus alvarezii, with various analyses of quality parameters (Noviani 2021; Barokah 2022). Nonetheless, the use of Gracilaria sp. flour to formulate other product, such as fish sausage, ekkado, and dry noodles, has been evaluated (Sipahutar et al. 2020a, b; Aditia et al. 2021). This paper will compare the results obtained with those of similar previous studies.
The lower trend in the F15 boba pearls at 2.17 kcal g− 1 compared to the control at 2.28 kcal g− 1 and the commercial sample of 2.38 kcal g− 1 shows the low calorific value of seaweed in general. According to Kailas and Nair (2015), Gracilaria sp. has a calorific value between 1.67–3.32 kcal g− 1. Previous studies also stated that high fiber and low lipid content might cause the low calorific content in seaweed (Rajapakse and Kim 2011; Rosemary et al. 2019). On the other hand, calorific value of tapioca flour was 4.31 kcal g− 1, as reported by Maust et al. (1972). The higher calorific content might correlate with the high starch proportion of 70% amylopectin and 20% amylose, along with less fiber content. This implies that tapioca flour is more digestible in human metabolism (Maust et al. 1972). Based on the results, Gracilaria sp. flour has great potential to reduce calorific content of boba pearls. Nevertheless, higher concentrations and other ingredient formulations need to be tested against calorific value in future studies.
The high total protein content in F15 at 1.75% DW compared to the control and commercial boba pearls with value of 1.41% DW and 0.97% DW respectively was possibly due to the high content of protein in Gracilaria sp. Álvarez-Viñas et al. (2019) reported that Gracilaria sp. has 0.6–45.0% DW of protein content. Another study characterizing seaweed Gracilaria sp. flour showed that the flour still contained 8.77% FW of protein (Munandar et al. 2019). In contrast, the protein content in tapioca flour was low (< 0.10% FW), as reported by Grace and Henry (2020).
In a study conducted by Sipahutar et al. (2020b), the increase in Gracilaria sp. flour proportion from 0 to 10% raised the protein content of fish sausages from 13.04 to 13.28% FW. Sipahutar et al. (2020a) also found that the protein content of fish ekkado added with 0–6% of Gracilaria sp. flour proportion increased from 17.81 to 19.50% FW, compared to the control with a value of 17.56% FW. However, Aditia et al. (2021) observed the opposite results, where the total protein content of dry noodles decreased from 12.52 to 10.58% FW with the substitution of Gracilaria sp. flour proportion between 0–25%. The reduction might be due to the increased moisture content of dry noodles from 50.38–54.57% FW with Gracilaria sp. flour proportion, diluting the protein content.
Gracilaria sp. not only contains a high quantity but also potentially possesses a high quality of protein. Previous studies indicated the high digestibility of the Gracilaria sp. protein (Álvarez-Viñas et al. 2019), which is essential for its absorption in the body. Gracilaria sp. potentially contains phycobiliproteins, which are pigment proteins valuable in food, cosmetic, and analytical chemistry sectors. Gracilaria sp. protein might comprise bioactive peptides that can be used as a supplement or medication against several diseases, such as hypertension, hepatitis, and diabetes (Francavilla et al. 2013; Álvarez-Viñas et al. 2019). The protein might also consist of a good proportion of Essential Amino Acids (EAAs) which have great benefits for human metabolisms, such as growth and immunity (Francavilla et al. 2013; Chan and Matanjun 2017; Rosemary et al. 2019). Therefore, adding the Gracilaria sp. flour could improve the health impact of boba pearls aside from their protein content. Given these potentials, further studies are needed to evaluate the bioactivities, pigment, and amino acid content.
The decreasing trend of the total lipid content from 1.01 to 0.39% DW with a higher proportion of Gracilaria sp. flour might due to the low lipid content of Gracilaria sp. According to Chan and Matanjun (2017) and Álvarez-Viñas et al. (2019), the lipid content in Gracilaria sp. is only around 0.3–7.1% DW. This information is also supported by the data on lipid content in Gracilaria sp. flour, which is 0.32% FW according to Munandar et al. (2019). On the other hand, the lipid content in tapioca flour was found to be low, at 0.19% FW (Grace and Henry 2020). This might explain the comparable lipid content between the F15 (0.39% DW) and commercial boba pearls (0.38% DW).
A similar lipid content trend was also found by Sipahutar et al. (2020a) and Aditia et al. (2021) who observed a decrease in fish ekkado and dry noodles lipid content from 5.84–2.34% FW and 0.64–0.44% FW respectively along with rising Gracilaria sp. flour composition. However, Sipahutar et al. (2020b) showed that the lipid content of fish sausage was not significantly affected by different flour fractions. This result might indicate the need to further test flour proportion for a better understanding of lipid and other proximate content trends.
Although Gracilaria sp. possesses low lipid content, it has a considerable amount of Polyunsaturated Fatty Acids (PUFAs). Previous studies reported that Gracilaria sp. has a balanced proportion of ω-6 and ω-3 PUFAs, which is < 10. A balanced ω-6 and ω-3 PUFAs ratio consumption can boost health by protecting the cardiovascular system, lowering blood cholesterols, and giving anti-inflammatory/anti-cancer effects (Francavilla et al. 2013; Chan and Matanjun 2017). Therefore, future studies must evaluate the composition of PUFAs and other fatty acids in Gracilaria sp.-based boba pearls.
Previous studies have pointed out the high ash content potential in Gracilaria sp., which is between 7.4 to 40.3% DW (Francavilla et al. 2013; Chan and Matanjun 2017; Álvarez-Viñas et al. 2019; Rosemary et al. 2019). This condition might have instigated the high ash content, especially in the F15 sample with 0.80% DW compared to the control which had a value of 0.66% DW. Munandar et al. (2019) reported a high ash content which amounted to 15.08% FW, while other studies found an increase in ash content in fish sausage (1.27 to 1.79% FW), fish ekkado (1.61 to 2.53% FW), and dry noodles (2.42 to 5.07% FW) with rising Gracilaria sp. flour proportion (Sipahutar et al. 2020a, b; Aditia et al. 2021).
This study also showed that the commercial boba pearls contained more ash with a value of 1.14% DW than Gracilaria sp. flour-based samples. However, Grace and Henry (2020) reported that the ash content in tapioca flour was low at 0.02% FW. This difference is due to the other ingredients in the commercial boba pearls which might also contribute to the ash content aside from tapioca flour.
The high ash content in Gracilaria sp. indicates its richness in minerals with the most abundant being K and Na as previously mentioned by Chan and Matanjun (2017). Gracilaria sp. has a low N/K ratio and the intake into the human body could lower the possibility of hypertension. Gracilaria sp. also contains other minerals, such as Mg, Ca, Fe, Zn, Cu, and Se, making it a potential mineral source for human nutrition needs (Chan and Matanjun 2017; Álvarez-Viñas et al. 2019; Rosemary et al. 2019). Therefore, it is necessary to evaluate the mineral content of Gracilaria sp. flour-based boba pearls in subsequent studies.
This study found that the F05, F10, and F15 samples had a higher trend of total carbohydrate content than the control. This result correlates with the high carbohydrate content nature of seaweed Gracilaria sp., which ranged from 24.8–78.7% DW as reported by Álvarez-Viñas et al. (2019). Sipahutar et al. (2020a) also found similar results, where adding a Gracilaria sp. flour proportion to fish ekkado increased the carbohydrate content from 19.10 to 20.19% FW. Furthermore, Grace and Henry (2020) reported that tapioca flour contains high carbohydrates of 89.04% FW. This characteristics might explain the higher total carbohydrate content in the commercial boba pearls compared to Gracilaria sp. flour-based samples.
Although Gracilaria sp. and tapioca flour contain high carbohydrates, they have different types. Tapioca flour carbohydrate consists mainly of starch estimated at 88.8% FW with low dietary fibers of 0.68% FW (Grace and Henry 2020). On the other hand, Gracilaria sp. carbohydrate is mostly agar ranging from 11.2–56.6% DW with high dietary fibers of 3.8–64.74% DW (Jung et al. 2013; Chan and Matanjun 2017; Álvarez-Viñas et al. 2019). Due to its composition, tapioca flour has a high glycemic potency, with a glycemic index (GI) of 85 (Grace and Henry 2020; Yusof et al. 2020). A food material with a GI of more than 69 is considered to have a high glycemic potency. Meanwhile, high glycemic potency food materials are not preferred from the health perspective, as they are digested rapidly by the human body, leading to a significant rise in blood glucose and the risk of diabetes (Lu and Chen 2022).
Conversely, seaweed including Gracilaria sp. potentially have a low glycemic potency (GI < 56) due to their high dietary fiber content. The human body digests a low glycemic potency food material more slowly, leading to a gradual and minor rise in blood glucose, with reduced risks of diabetes (Grace and Henry 2020; Kaur et al. 2022; Lu and Chen 2022). The high dietary fiber of seaweed means it will hardly be absorbed and used by the human body. Seaweed dietary fiber consists of water-soluble fibers such as agar and insoluble fibers including cellulose (Jung et al. 2013; Lu and Chen 2022). According to Chan and Matanjun (2017), Gracilaria sp. has a soluble: insoluble dietary fiber ratio of 1:2.5, which is close to the standard value of 1:2 in food manufacturing. A food material with a good ratio of soluble: insoluble dietary fiber can be used to prevent and treat several diseases, such as diabetes as well as cardiovascular illness. Given the low glycemic potential, it is essential to evaluate the dietary fiber content and post-prandial Glycemic Responses (GR) of Gracilaria sp. flour-based boba pearls in subsequent studies.
The higher trend of moisture content in Gracilaria sp. flour-based boba pearls compared to the control might be related to the high moisture nature of Gracilaria sp. According to a previous study, Gracilaria sp. contains 12.5–19.2% FW of moisture (Rosemary et al. 2019), while Gracilaria sp. flour had a moisture content of 11.83% FW (Munandar et al. 2019). As previously discussed, Gracilaria sp. also has a high hydrocolloid, fiber, and protein content. These molecules have a water-binding capacity, which leads to the high moisture content in the sample (Chan and Matanjun 2017; Sipahutar et al. 2020b; Aditia et al. 2021). Sipahutar et al. (2020a) and Aditia et al. (2021) found similar results, where adding Gracilaria sp. flour proportion to fish ekkado and dry noodles also increased the moisture content from 50.38–54.57% FW and 5.78–10.62% FW respectively.
The lower trend of moisture content in the commercial boba pearls did not correspond with the result of the tapioca flour. According to Grace and Henry (2020), tapioca flour contains moisture of about 9.97% FW. The low moisture content in the commercial sample might be because boba pearls have been optimized to increase their shelf life (Aditia et al. 2021). High moisture content in food must be avoided to slow down microorganism growth and provide a longer shelf life. Given that water interacts with chemicals such as protein and hydrocolloid, as well as microorganisms, and components related to food materials, moisture content could affect quality and sensory parameters of boba pearls (Chan and Matanjun 2017; Waqiah et al. 2019; Aditia et al. 2021; Sipahutar et al. 2021).
The pH of all Gracilaria sp. flour-based boba pearls samples, namely 5, can be considered low or acidic. Mohibbullah et al. (2023) found that the addition of seaweed Ulva intestinalis powder with a proportion of 0–5% to make cookies decreased the pH of product from 6.59 to 6.51. They suggested that the polysaccharides and phenolic compounds with carboxyl and sulfate groups content in U. intestinalis contributed to the low pH of cookies. The pH results of this study might be coherent with the literature, although with different types of seaweed. However, Widati et al. (2021) had a contradicting result wherein the addition of seaweed Eucheuma cottonii flour with a proportion of 0–7.5% to beef meatball increased the pH of product from 5.94 to 6.07. The increase was probably due to the alkaline minerals including Na, K, Ca, and Mg contained in E. cottonii. According to previous studies, Gracilaria sp. has various bioactive compounds with health benefits including sterols, phenols, phycobiliproteins, and carotenoids that might affect the pH of product (Francavilla et al. 2013; Chan and Matanjun 2017; Álvarez-Viñas et al. 2019). Therefore, the bioactive components in Gracilaria sp. flour-based boba pearls should be assessed to validate the result in subsequent studies.
The control and commercial boba pearls also had a low pH of 4–5 which might correlate with the pH of tapioca flour. As mentioned by Hasmadi et al. (2020), the typical pH of tapioca flour is 5.5–8.5. Yusof et al. (2020) formulated boba pearls from sweet potato (Ipomoea batatas) flour and found that the pH of product was low with value ranging from 5.41–5.71, due to acidic compounds present including ascorbic acid. Similarly, tapioca flour might also contain acidic compounds that reduced the pH of the control and commercial boba pearls. The pH obtained can support a longer shelf-life by preventing the growth of food spoilage bacteria. For instance, Clostridium botulinum cannot grow optimally at a pH below 4.6 (Yusof et al. 2020).
As previously discussed, the low pH of flour-based boba pearls might be caused by the bioactive compounds in Gracilaria sp. Maftuch et al. (2016) and Fadhlullah et al. (2022b) reported that bioactive compounds such as alkaloids, flavonoids, tannins, and phenols have antibacterial activity against Staphylococcus aureus, Aeromonas hydrophila, and Pseudomonas putida. This information explains the decreasing trend of microbial concentration of boba pearls in this study, along with a rise in the proportion of Gracilaria sp. flour. Pasteurization and sealed filling can also be carried out to prevent microbial growth in further product development (Liu et al. 2021).
The sensory acceptance rate of all Gracilaria sp. flour-based boba pearls was in the slightly like category for all the parameters including aroma, taste, texture, and appearance, which was not different from the control. The slightly better result of the taste and texture for the commercial sample was possibly due to the optimization of the ingredients by the manufacturer, such as sweetener addition, surface coating, and proper drying (Yusof et al. 2020). This result indicates that Gracilaria sp. flour-based boba pearls formulation still needs improvement to be accepted by the market regarding the sensory parameters.
Several factors must be considered to improve the sensory characteristics of Gracilaria sp. flour-based boba pearls. According to Bubin et al. (2019) and Sipahutar et al. (2021), the acceptance level of boba pearls appearance is affected by the surface structure including factors such as smoothness, consistency, thickness homogenous level, and color. Bubin et al. (2019) also reported that hydrocolloid proportion could affect the surface structure of boba pearls. For instance, boba pearls containing sodium alginate and iota carrageenan tend to form a gel with higher cross-linking, making the surface appear less smooth, with more folds and unevenness. Also, samples with low moisture content retention tend to appear with a rougher surface, cracks, and porous after storage. Gracilaria sp. flour used in this study contains agar, a hydrocolloid, as well as pigments such as chlorophyll and carotenoids, which can affect the color of boba pearls. According to previous studies, a high Gracilaria sp. flour proportion produced darker product which were less preferred by the panelists (Aditia et al. 2021; Sipahutar et al. 2021; Mohibbullah et al. 2023). Therefore, this information must be considered to improve the appearance of Gracilaria sp. flour-based boba pearls.
The ideal boba pearls texture should be soft enough to be easily ruptured by optimal chewing perception. The textural properties consist of hardness, cohesiveness, gumminess, springiness, rupture force, and elasticity. Previous studies showed that the best boba pearls textural properties were those having a low hardness, cohesiveness, and rupture force, with high springiness (Bubin et al. 2019; Kaur et al. 2022). Therefore, the textural properties of Gracilaria sp. flour-based boba pearls should also be evaluated in future studies.
Although Gracilaria sp. flour contains agar, a gelling agent (Sipahutar et al. 2021), it is crucial to ensure that the flour can blend well with other ingredients for complete gelatinization. As previously discussed, Gracilaria sp. flour also contains low starch, as well as high protein and dietary fiber content. On the other hand, Kaur et al. (2022) reported that flour with lower starch, higher protein, and higher dietary fiber contents tends to decrease the gelatinization level and produce boba pearls with greater hardness. Additional binders, such as sago starch, can improve the blending and gelatinization of boba pearls (Kaur et al. 2022) but their calorific value must be considered carefully.
Due to high mineral content, Gracilaria sp. tends to have a fishy odor (Fadhlullah et al. 2022b; Mohibbullah et al. 2023), which reduced the aroma and taste acceptance by the panelists. The odor can be prevented by thoroughly washing before milling Gracilaria sp. into flour (Sipahutar et al. 2021). In this study, cocoa powder was added to improve the taste and aroma of the samples, while Yusof et al. (2020) improved the aroma and taste of sweet potato-based boba pearls by adding brown sugar. However, additional sweeteners must be from natural sources with low calorific content to fulfill the health purpose.