Nowadays, over the global there is a great interest to obtain pectinase from cheap and suitable substrates like agricultural residues.
Here the efficiency of P. indica in biodegradation of SBP has been evaluated. Subsequently, the polygalacturonase activity on SBP+ and SBP− media has been reported for 10 days (Fig. 1). The polygalacturonase production and fungal growth reached the maximum level simultaneously on both medium. It’s stablished that the components of the medium have great effect on the induction of pectolytic enzymes. Several substances play an inducer role on these enzymes synthesis (Nair &Panda 1997). The utilization of agro-industrial residues, like apple pomace and sugar beet pulp, further could solve environmental problems of the by-products (Heerd et al. 2014). The choice of perfect agricultural residue to induce enzyme production depends on several factors, such as cost and availability of the substrates. It is known that duration of fermentation depends on the medium composition, organism, concentration of nutrients and the physiological conditions (Patil &Dayanand 2006).
SBP has been used as raw material to induce pectinase production by Aspergillus niger. Additionally it has been used as carbon source as well as pectinase inducer to produce extracellular alkaline pectinase, by Bacillus gibsoni, under SSF (Jacob 2009). Cultivation of T. reesei Rut C-30 on sugar beet pulp (50 g/L), the protein content, pectinase activity and specific activity reached their maximum value after 60 h of fermentation (0.43 g/l, 0.82 U/ml and 1.9 U/mg respectively) (Olsson et al. 2003). The highest enzyme activity by A. sojae on 30% sugar beet pulp as an inducer and wheat bran as medium wetted agent attained after 8 days (Heerd et al. 2014).
However our results show the highest activity of exo-pectinase in medium containing sugar beet pulp determined 3.4 U/mL on 96 h of fermentation and following optimization it reaches to 19.41 U/ml.
The greatest endo- and exo-pectinase activity by A. niger from sunflower head in SSF (5.1U/g and 17.1U/g) and SmF (4.5 U/ml and 16.0 U/ml) were measured on 96 h. According to the different studies about the fermentation time, it exhibited wide range 40–120 h and 90–120 h in submerged and solid state fermentations, respectively (Patil &Dayanand 2006).
The Colletotrichum isolated from Argentinian soybean, yielded high amount of the PG (1.08 U/ml) after 7–10 days of incubation and coincide with maximum growth. In medium involving glucose as a sole carbon source decreased polygalacturonase production was monitored (Ramos et al. 2010).
Environmental and nutritional factors are known as two essential factors which affect enzyme production by microorganisms. The pectin and polygalacturonic acid applied as only source of carbon in the medium which induced synthesis of pectinolytic enzymes by A. niger and there was no pectolytic activity in medium containing glucose as an only carbon source. Production of pectin degrading enzymes in the presence of pectin and high glucose concentrations were inhibited although glucose in low concentrations promoted their production. The observed low pectinolytic activity in media with high glucose concentrations is possibly due to provide growth need of organism by the glucose consumption and caused to decrease the pectin lysis. Furthermore, at low glucose concentrations, high pectolytic activity were observed (Fawole &Odunfa 2003). In agreement with Fawole et al, Our results showed the highest pectinolytic activity was attained at the lowest glucose concentration (60 g/L).
Pectinolytic activity by A. niger on medium containing pectin, poly galacturonic acid and glucose at 30◦C for 5 days was 17.2, 13.8 and 0 U/ml, respectively (Fawole &Odunfa 2003).
As it is shown by Aguilar and Huitron (1987) high exogenous glucose and galacturonic acid could be influenced endo-PG enzyme production by catabolite repression, whereas glucose had no effect on the exo-PG. The Glucose concentration above 10% (w/w) in the SSF, decreased noticeably the activity of endo and exo-PG (Aguilar &Huitrón 1990).
In Solis-Pereyra et al study, exo-PG/gdm and endo-PG/gdm activity by A. niger on medium containing 16% (w/w) citric pectin, were 281 U and 152 U. Moreover, inhibited enzyme production and growth were detected on 20- 30% (w/w) pectin concentration (Fontana et al. 2005).
Ammonium sulphate was introduced as the favourable nitrogen source for pectinase production by A. niger (Fawole &Odunfa 2003). Our results are in concurrence with the observations of Sapunova who also demonstrated that ammonium salts could act as stimulator of the pectinase. It has been described that nitrogen limitation decreases the production of polygalacturonase (Thakur et al. 2010).
Bai and et al, examined the impact of different nitrogen sources on pectinase induction and great enzyme activity measured with ammonium sulfate, yeast extract, soya peptone, soya pulp and MGW(Bai et al. 2004).
Patil and et al examined the impact of ammonium phosphate and sulphate on pectinase production by A. niger from sunflower head in both SSF and SmF. As their study revealed, ammonium phosphate and sulphate could increases the production of pectinase in both fermentation conditions. However, this increase was very less with ammonium phosphate in comparison to ammonium sulphate. The maximum production of endo-pectinase and exo-pectinase by DMF 27 were recorded in SmF condition 18.9 U/ml and 30.3 U/ml respectively (Patil &Dayanand 2006).
As stated in many studies the average molecular mass of polygalacturonase are in the range of 35-80 KDa (John et al. 2020). Different microbial species produced different molecular mass of pectinase enzyme. Different factors such as the substrate, nature of microorganism, host cell wall and analytical methods results in different mass of pectinase (Oyede, 1998). The molecular weight of P. indica polygalacturonase in our study was comparable with previous reports.