P. Selvakumar

Recent Developments in Microbial Inulinases Its Production, Properties, and Industrial Applications

Microbial inulinases are an important class of industrial enzymes that have gained much attention recently. Inulinases can be produced by a host of microorganisms, including fungi, yeast, and bacteria. Among them, however, Aspergillus sp. (filamentous fungus) and Kluyveromyces sp. (diploid yeast) are apparently the preferred choices for commercial applications. Among various substrates (carbon source) employed for their production, inulin-containing plant materials offer advantages in comparison to pure substrates. Although submerged fermentation has been universally used as the technique of fermentation, attempts are being made to develop solidstate fermentation technology also. Inulinases catalyze the hydrolysis of inulin to d-fructose (fructose syrup), which has gained an important place in human diets today. In addition, inulinases are finding other newer applications. This article reviews more recent developments, especially those made in the past decade, on microbial inulinases—its production using various microorganisms and substrates. It also describes the characteristics of various forms of inulinases produced as well as their applications.

Solid state fermentation for the synthesis of inulinase from Staphylococcus sp. and Kluyveromyces marxianus

Solid state fermentation was carried out for the production of inulinase from Staphylococcus sp. RRL-1 and Kluyveromycesmarxianus ATCC 52466. Wheat bran, rice bran, coconut oil cake and corn flour, individually or in combinations were tested for their efficiency to be used as the solid substrate. Both cultures grew well in a wheat bran medium. Although the yeast culture produced relatively higher enzyme yields, the bacterial culture took a relatively shorter time to attain maximal yield. Under optimized conditions, the extra-cellular enzyme concentration reached a peak in 48 h with Staphylococcus sp. (107.64 U of inulinase per gram dry fermented substrate-gds) and in 72 h with K. marxianus (122.88 U/gds). This is the first report on inulinase production in SSF.

Biosynthesis of glucoamylase from Aspergillus niger by solid-state fermentation using tea waste as the basis of a solid substrate

Tea waste, supplemented with minerals, was used as the solid substrate for the synthesis of glucoamylase by a strain of Aspergillus niger NCIM 1248. Maximum glucoamylase synthesis [198.4 IU/g dry substrate (gds)] was obtained on the mineralised tea waste at 96 h with an inoculum, initial moisture and pH of 4%, 60% and 4.5, respectively at 30°C. Among different carbon sources, sucrose favoured the increase of glucoamylase synthesis (212.6 IU/gds) in 96 h, whereas among different nitrogen sources, malt extract gave the highest enzyme titre (226.0 IU/gds) at 72 h.

Comparative studies on inulinase synthesis by Staphylococcus sp. and Kluyveromyces marxianus in submerged culture

Staphylococcus sp. RRL1 and Kluyveromyces marxianus ATCC 52466 produced extra-cellular inulinase when grown in liquid medium containing inulin as the sole carbon source and the former produced about 30% more enzyme activity. The highest inulinase activity (618 U/liter) from Staphylococcus sp. was obtained in a medium with an initial pH, temperature, agitation and the size of inoculum of 6.5, 37°C, 150 rpm and 4%, respectively. Kluyveromyces marxianus ATCC 52466 gave highest inulinase activity (470.4 U/liter) in a medium with an initial pH, temperature, agitation and size of inoculum as 6.0, 30°C, 150 rpm and 4%, respectively. The Staphylococcus sp. seems to be a new and useful source of inulinase.

Copra waste : a novel substrate for solid-state fermentation

Abstract Solid-state fermentations were carried out to evaluate the feasibility of copra waste being used as a solid substrate for production of glucoamylase enzyme by Aspergillus niger NCIM 1245. The waste supported mould growth and enzyme activity, and under optimised conditions enzyme units as high as 194 IU/g dry fermented substrate were produced when fermentation was carried out for 96 h at 30 + 1°C with an initial substrate pH and moisture of 4·5–4·7 and 65%, respectively. Addition of inorganic nitrogen enhanced the enzyme yields without affecting dry matter loss significantly.

Performance of a column bioreactor for glucoamylase synthesis by Aspergillus niger in SSF

Abstract A novel bioreactor was developed for glucoamylase production in solid state fermentation using Aspergillus niger . Glass columns of different diameter were placed vertically and packed with pre-inoculated substrate and with substrate bed heights in the range 4.5–22.0 cm. Moist air was passed through the bottom of the bioreactor at 1–1.5 vvm and fermentation was carried out for 48 h at 30 ± 1°C. A column packed to a bed height of 18 cm produced about 50% more enzyme (in 48 h) than flask experiments. There was a significant difference between different segments of the columns in growth, enzyme synthesis and sporulation pattern.

Culture conditions for production of 2-1-β-D-Fructan-fructanohydrolase in solid culturing on chicory (Cichorium intybus) roots

Investigations were carried out to optimize the culture conditions for the production of b-D-fructan-fructanohydrolase by an indigenously isolated bacterial culture of Staphylococcus sp. RRL8. Experiments were carried out in solid culturing using chicory roots (powdered) as the source of carbon, which was supplemented, with corn steep liquor and potassium dihydrogen phosphate. A number of process parameters, like period of cultivation, initial moisture content in the substrate and temperature of incubation were optimized. Maximum extra-cellular enzyme was produced when fermentation was carried out at 30oC for 24 h using chicory roots with 60% initial moisture. Supplementation of the substrate with additional carbon source (except with sucrose) resulted decreased enzyme titres, which indicated that the strain was partially depressive. Addition of external nitrogen sources (in addition to corn steep liquor) also failed to stimulate enzyme formation; rather exerted harmful impact on bacterial culture of Staphylococcus sp. RRL8.

Inulinase synthesis from a mesophilic culture in submerged cultivation

A newly isolated mesophilic bacterial strain from dahlia rhizosphere, identified as Staphylococcus sp. and designated as RRL-M-5, was evaluated for inulinase synthesis in submerged cultivation using different carbon sources individually or in combination with inulin as substrate. Inulin appeared as the most favorable substrate at a 0.5–1.0% concentration. Media pH influenced the enzyme synthesis by the bacterial strain, which showed an optimum pH at 7.0–7.5. Supplementation of fermentation medium with external nitrogen (organic and inorganic) showed a mixed impact on bacterial activity of enzyme synthesis. The addition of soybean meal and corn steep solid resulted in about an 11% increase in enzyme titers. Among inorganic nitrogen sources, ammonium sulfate was found to be the most suitable. Maximum enzyme activities (446 U/L) were obtained when fermentation was carried out at 30°C for 24 h with a medium containing 0.5% inulin as a sole carbon source and 0.5% soybean meal as the nitrogen source. Bacterial inulinase could be a good source for the hydrolysis of inulin for the production of d-fructose.