Estimation of Saccharomyces cerevisiae Biomass Cultured in Cassava Mill Effluents

Yeast is a unicellular microorganism that belongs to the division of Ascomycota and Fungi imperfecti [1]. Several species of yeast exist. Some of the common genera of yeast include Rhodotorula, Candida, Trichosporon, Saccharomyces, Kluyveromyces, Pichia, Trichospora, Torulopsis, Leucosporidium, Hansenula, Torula, Cellulomonas, Xanthomonas and Schizosaccharomyces [1,2]. Like bacteria and mould, some species of yeast are pathogenic to humans especially on immune-compromised individuals. While several species play beneficial roles in humans health as well. Saccharomyces cerevisiae is among the grass organisms that have been implicate with food safety. Like some species of Lactobacillus, Saccharomyces cerevisiae have several foods and feed potentials [2,3]. Reethus et al. [3] reported that Saccharomyces cerevisiae is mainly used in animal, while Saccharomyces boulardii is the most commercially used probiotics (a live microbial feed supplemented to animal diets to enhance the balance of microbes found in the intestines). Saccharomyces cerevisiae are widely used in fermentation processes of sugar rich substances such as cassava wastes [4,5], grapes, sugarcane, fruit wastes [3].

Saccharomyces cerevisiae can be cultivated under aerobic and anaerobic condition depending on the choice of medium. Saccharomyces cerevisiae have the potentials to utilize and grow in diverse sugars especially glucose, sucrose, maltose etc. [3]. Several substrates have been used for the cultivation of Saccharomyces cerevisiae including cassava mill effluents [6-9], palm oil mill effluents [10], jagger, pods, fruit wastes, vegetable wastes, banana and orange peels and deoiled cake [3]. Specifically, Nigeria is the largest producers of cassava in the world [4,11,12]. During the processing cassava mill effluents (waste water) is a major liquid wastes that are discharged into the soil without any form of treatment [6-9,13-16]. Thereby causing an alteration in microbial [17] and physicochemical constituents of the receiving soil over a prolong period of time [12]. Studies have indicated that the constituents of the wastes could be improved upon when treated with Saccharomyces cerevisiae [6,13].

Saccharomyces cerevisiae cultured in cassava mill effluents contain additive such as palm oil and some level of heat treatment is known to reduce to reduce cyanide content (a major toxicant of cassava) [7], and contain amino acid and proximate composition [8]. Furthermore, Bekatorou et al. [1] reported that Saccharomyces cerevisiae is rich in nutrients including proximate composition, minerals (including essential heavy metals and cations), vitamins. Probably due to the role of Saccharomyces cerevisiae in animal feed and its industrial application, there is the need to estimate the quantity of Saccharomyces cerevisiae biomass from cassava mill effluents.

Sample collection

Raw cassava mill effluents containing additive such as palm oil were obtained from a cassava mill in rural community in Delta state, Nigeria. The samples were collected in triplicates. The samples were properly labeled and packaged in an ice crest prior to transportation to the laboratory.

Saccharomyces cerevisae isolation and identification

S. cerevisiae used was bought from palm vendor in Rumuomasi, Port Harcourt, Rivers state, Nigeria. The Saccharomyces cerevisiae were isolated following pour plate techniques previously described by Benson [18], Pepper and Gerba [19]. The Potato dextrose agar used was supplemented with chloramphenicol. The resultant microbial isolates were streaked in another Potato dextrose agar plate containing chloramphenicol. The identification of the isolates were based microbiological techniques (i.e. cultural, morphological, and physiological/biochemical characteristics) including carbon fermentation and assimilation, glucose-peptone-yeast extract broth, lacto-phenol cotton blue stain and growth based on temperature as previously described by Kurtzman & Fell [20], Benson [18], APHA [21] and have been applied by Abioye et al. [22], Iwuagwu & Ugwuanyi [10], Okoduwa et al. [23]. The characteristics of the identified isolates were compared with the scheme of Ellis et al. [24].

Biomass cultivation

Wastewater treatment method previously described by Abioye et al. [22], Okoduwa et al. [23] was modified and used for the cultivation of biomass as previously described by Izah et al. [6-9]. Approximately 10.0ml of the cultured Saccharomyces cerevisiae inoculum were aseptically introduced into 100ml of sterile cassava mill effluents in 250ml Erlenmeyer’s flask. The flask was capped with cotton wool wrapped with aluminum foil paper. The flasks were intermittently shaked between 7.00-19.00 hours. The incubation period lasted for 15 days. During which the about 60ml of the effluents were decanted while the remaining 40ml were filtered through Whatman filter paper. The biomass recovered was washed with distilled water before re-filtering. The final sludge trapped in the filter paper was oven dried, and weighed.

Statistical analysis

The results were expressed as mean±standard deviation using SPSS software version 20.

The Saccharomyces cerevisiae biomass recovered at the end of the experiment was 3.93±0.55g/L. The value produced was lower than the values reported by previous authors. Some of these values are 4.42 g/L obtained from the culturing of Saccharomyces species in palm oil mill effluents [10], 4.0g/l obtained from culturing of Aspergillus niger in palm oil mill effluents [25], 7.5g/l obtained from culturing of Rhodotorula glutinis in palm oil mill effluents [26].,Reethus et al. [3] reported biomass of Saccharomyces cerevisiae MTCC 174 and Saccharomyces cerevisiae MTCC 3821 as 6.60g/l and 6.74 g/l. respectively for jagger, 4.20g/l and 4.29g/l, respectively for pods, 4.88g/l and 4.94, respectively for fruits wastes. The studies of the authors for vegetable wastes, banana peels, orange peels and deoiled cake has a yield of 3.72g/l, 3.81g/l, 3.35g/l and 3.69g/l, respectively (Saccharomyces cerevisiae MTCC 174), and 3.63g/l, 3.80 g/l, 3.54 g/l and 3.77 g/l, respectively (Saccharomyces cerevisiae MTCC 3821) and this results were in consonance with the work of this study. The variations could be due to environmental conditions such as temperature and pH of the effluents used. Furthermore, the physical, chemical and microbial concentration of the effluents could also affect the biomass productivity. Ogbonda et al. [27] reported that pH and temperature could affect the yield of Spirulina species isolated from oil polluted estuarine.

This study showed Saccharomyces cerevisiae biomass yield of 3.93g/l. This suggests that cassava mill effluents are a promising feed stock for the cultivation of Saccharomyces cerevisiae biomass. In addition, during the cultivation some of the pollution indicators such as chemical oxygen demand and pH can be improved upon. Therefore studies should be focused on possible optimization of the biomass through manipulation of the environmental conditions.

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