A screening method for detection of α-galactosidase-producing microorganism had been studied. Similar to ours, findings by Youssef et al. (2006), Hossain et al. (1996), and Lin and Chen (2004) have isolated the Aspergillus fungal cultures for β-mannanase activity using copra meal as a carbon source for cultivation. The biotechnological applications of α-galactosidase includes the removal of raffinose family oligosaccharides (RFOs) in soymilk, beet sugar industry, flatulence, blood group conversion, etc. (Raja et al. 2020; Bhatia et al. 2019).
Carbon occupies a unique position among the essential elements required by microorganisms. When it is consumed, it undergoes three metabolic changes, viz., conversion into cell substances, carbon dioxide and accumulation in several metabolic products. Based on the type and nature of carbon source in the medium, the organism tries to grow and thus produces number of enzymes.
Similarly, Lin and Chen (2004) have made observation that fourfold enhanced production of mannanase by growing A. niger in medium containing 2% defatted copra meal. Therefore, based upon the same amount of carbon sources, the defatted copra carried the higher mannan content, which would induce more enzyme production by the microorganisms. Copra waste was apparently a better substrate because of its high reducing sugar content. Defatted copra also contained more protein and minor elements, which were more beneficial to fungal growth than other carbon sources. The medium must be designed to provide the essential elements carbon, nitrogen, sulfur, oxygen, phosphorous, magnesium, calcium, and numerous other trace elements such as iron, copper, cobalt, zinc, manganese, and molybdenum, which may be required to support active culture function. However, it is highly important in formulating an effective medium for use in a competitive enzyme production process to produce one which is both cheap and where possible, reproducible over a long production period. These relate to the phenomenon of induction, catabolite repression, and end product inhibition and in case of extracellular enzymes and protein release mechanisms.
Similar to our findings, Anisha (2017) have reported highest α-galactosidase obtained in submerged fermentation on various carbon sources.
The mechanisms that govern the formation of extra cellular enzymes are influenced by the availability of precursors for protein synthesis. Furthermore, the nitrogen source can significantly affect the pH of the medium during the course of fermentation (Lin and Chen 2004). Nitrogen is the principal element governing cell formation and synthesis of various constituents. It influences the synthesis of various enzymes especially in microorganisms, which are either accumulated inside the cell or excreted into the culture medium. The type of nitrogen and also its concentration influences markedly the yield and the rate of enzyme production.
These results are in concordance with the data of many investigators, who have reported that fungi produce more enzymes on addition of complex organic nitrogen sources (Anisha 2017; Naganagouda et al. 2009). Concerning the inorganic nitrogen sources used as shown in Table 2, a maximum activity was observed with ammonium nitrate in the Penicillium sp. (6.325 U/ml). In case of organic nitrogen sources, a maximum activity was observed with yeast extract rather than peptone, beef extract, casein, and soybean meal (Table 2), respectively. In addition yeast extract showed a maximum production comparable with different inorganic nitrogen sources.
Among several cultural parameters influencing the product formation by microorganisms, the hydrogen concentration of the culture medium is considered extremely important. The higher concentration of hydrogen or hydroxyl ions exhibits the growth of microbial culture and thereby influence the yield of enzyme or metabolite production. There are distinct three types of microorganisms according to their tolerance of hydrogen and hydroxyl ions. These are acidophilic, alkalophilic, and mesophillic strains which grow at varying ranges of pH in the cultivation medium.
The influence of age of the culture is very important in influencing the growth as well as product formation either extracellular or intracellular under shake or stationary conditions of fermentation.
Denaturation of enzyme possibly due to prolonged incubation could be the reason. Lin and Chen (2004) have compared time course of β-mannanase production by Aspergillus niger in shake cultures. They further reported that in shake culture 2nd day maximum activity was obtained.
α-Galactosidase produced by the genus Penicillium sp. and indeed most fungi have pH optima within the range of acidic pH ranging from 2.5 to 6.0. Slightly acidic pH optima of the enzymes of the present investigation match the values characteristic for the fungal glycoside hydrolases (Christov et al. 1999).
α-Galactosidases from various fugal sources exhibit acidic pH optima and several fungal α-galactosidases are stable over a wide range of pH (pH 3–12), which is a favorable property for biotechnological applications (Cao et al. 2009; Janika et al. 2010; Katrolia et al. 2012).
α-Galactosidase produced from mesophilic and thermophilic fungi adapted to wide range of temperatures ranging from 50 to 65 °C (Kotiguda et al. 2007; Simerska et al. 2007; Rezessy-Szabo et al. 2007; Viana et al. 2009).
Similar to our findings several researchers reported that thermostable α-galactosidases are useful in food processing and other biotechnological applications, where operational conditions can denature thermo-labile enzymes (Brouns et al. 2006; Pessela et al. 2007).
Generally, metal ions have been shown to be relevant in enzyme activity. It has been reported that some metal ions such as Ag+, Cr+3, Cu+2, Fe+3, Hg+2, Mn+2, Pb+2, and Zn+2 inhibited α-galactosidase activity (Gote et al. 2006; Álvarez-Cao et al. 2018).