Volume 6, Issue 3, June Issue - 2018, Pages:482-489
|Authors: B. H. Joshi, R. M. Dhingani, R. V. Prasad|
|Abstract: Sustainable production of ethanol as alternative renewable fuels, there is a need for a yeast strain which can convert the non-food substrate into ethanol economically. Extensive screening program for such yeast for bioethanol production was attempted from the diverge ecosystem. That resulted into isolation of a yeast strain, designated strain ETDLT1, which was capable of ethanol fermentation using lactose as carbon source even at elevated temperatures. Beside this the strain is ethanol tolerant up to 12 %. The lactose fermentation performance of selected ETDLT1 strain was evaluated. It was found to produce 28 g/l of ethanol with yield of 0.36 %. (p/s, g/g). In laboratory fermentation ETDLT1 strain found significant potential for its ability for bioconversion of dairy processing wastes rich in lactose into ethanol in single step fermentation. Therefore, it was further selected for thorough characterization. Results of characteristics confirm the ETDLT1 isolate as the strain of Kluyveromyces marxianus.|
|Full Text: 1 Introduction Sustainable and economical production of ethanol or alternative renewable fuels are becoming increasingly important due to the limited supply of fossil fuels and the environmental consequences associated with their consumption (Balat, 2011; Binod et al., 2010). Present attention has been focused on development of alternative feedstock for its bioconversion into ethanol using potential microorganisms e.g., plant biomass or non-food waste, into useful compounds including ethanol, has already been recognized. Intensive research is being carried out to establish robust and economically feasible processes for production of bioethanol (Wyman, 1999). However, initial complex pretreatment of such substrates for its conversion into fermentable sugars is key problem need to be addressed by cost effective process. Carbohydrate rich waste generated by food industries could be serves as alternative feed stocks for its bioconversion using microorganisms into commercially important products. About 165 million tons of whey production is estimated worldwide. Out of which, about 95 % whey is contributed by cheese production. In India, chhana and paneer is major source of whey. Due to nutrient-rich nature, the whey has been emerged as alternative feedstock for microbial fermentations (Liu et al., 2016). Cheese whey, the main dairy by-product, is increasingly recognized as a source of many bioactive valuable compounds. Nevertheless, the most abundant component in whey is lactose (ca. 5% w/v), which represents a significant environmental problem. Technology is available to recover the protein from the whey, but, no adequate method is available for the utilization of whey lactose. Thus, it becomes necessitate to develop some strategy for valorization of whey lactose into marketable products. Due to the large lactose surplus generated, its conversion to bioethanol has long been considered as a possible solution for whey management (Guimaraes et al., 2010; Minakshi & Shilpa, 2012). The search of microorganism that efficiently ferments lactose has a high biotechnological interest, particularly for cheese whey management with simultaneous bioethanol production. Yeasts, particularly Saccharomyces spp., are the most common ethanol producers employed in industry (Edgardo et al., 2008). The fermentation of whey lactose to ethanol, particularly using yeasts, has been frequently referred in the literature, since at least the 1940s (Whittier, 1944; Rogosa et al., 1947; Webb & Whittier, 1948). Although the yeasts that assimilate lactose aerobically are widespread, those that ferment lactose are rather rare (Fukuhara, 2006), including e.g. Kluyveromyces lactis, K. marxianus, and Candida pseudotropicalis. The conversions of the lactose in cheese whey or whey permeate into fuel ethanol represents an advantage of whey over food-related fermentation feed stocks, such as corn, for ethanol production. Although, the viability of such bioprocessing is largely depends on its cost economics. Ethanol fermentation is affected by temperature rises during hot climates. In India, ambient temperature of 40°C and above is common in summer months. This requires cooling to maintain the temperature, which is not yet economically viable. However, the problem could be alleviated by using thermotolerant strains of yeast, which could capable to grow and produced ethanol at elevated temperatures. Other than thermotolerance, broad substrate utilization ability, higher saccharification rate, ethanol yieldand low energy requirement are the desirable traits for the successful exploitation of yeast for ethanol production (Dung et al., 2012; Kumar et al., 2013; Arora et al., 2015; Scully & Orlygsson, 2015). Therefore, the selection of the yeast strain is very crucial for bioconversion of different feedstock into ethanol. Present work was carried out to select an efficient thermotolerant yeast strain for valorization of lactoseat elevated temperature into ethanol. 2 Materials and Methods 2.1 Isolation and primary screening of yeast Yeast was isolated from the different habitats during screening program conducted for present study. Total of sixty seven samples were collected from food products as well as food industrial waste. The procured samples were used to isolate yeast using direct as well as enrichment method. Isolates obtained were screened out for its ability to produce ethanol, tolerance to elevated temperature and higher concentration of ethanol (Joshi et al., 2017). 2.2 Secondary screening for β-galactosidase activity Secondary screening of the selected yeast isolates based on its ability to produce β-galactosidase enzyme was carried out. The yeast isolates were activated by inoculating single colony in yeast extract peptone dextrose broth. Then it was incubated at 35°C for 30 h using shaker (120 rpm). Each of these activated isolates was streaked on lactose agar plates and incubated at 35°C for 48-72 h. Well grown colonies from lactose agar plate was inoculated in 2 ml of yeast extract peptone lactose medium containing 0.5 % yeast extract, 1 % peptone, 8 % lactose and pH 5.6 and incubated at 35°C overnight using orbital shaking at 120 rpm. Once the optimal growth was obtained, it was used for quantitative estimation of β-galactocidase activity using ONPG as substrate (Gupte&Nair, 2010). The unit activity of β-galactosidase enzyme was calculated using following formula: |
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