Background of Fermented Cashew Apple Juice

Alcoholic Fermentation

Alcoholic fermentation was the first process studied by applying cashew apple juice as a substrate due to its high content of reducing sugars, which are readily fermentable sugar. However, there are only a few studies on fermented beverages produced from cashew apples. Cashew apple wine was produced by Mohanty et al. (2006) using fully ripened and undamaged cashew apples.

The apples were processed just after the harvest. Cashew apples were cleaned by washing in tap water and by immersing for 3 days in 5% salt solution to reduce tannin content, after which they were steamed for 15 minutes at a pressure of 15 lb. The apples were then crushed in a mixer and grinder (TTK Prestige, Ltd., Bangalore, India) and the juice was extracted by using a juice squeezer.

The juice (must) was filtered through a cotton cheesecloth at 12°Brix and was treated with sodium metabisulfite (100 mg/mL) to inhibit the growth of undesirable microorganisms such as acetic acid bacteria, wild yeasts, and molds. Then, cane sugar and tartaric acid were added into the juice (amelioration) to attain 17°Brix and pH 3.6, respectively.

The ameliorated must was inoculated with 2% (v/v) starter culture (prepared with grape juice) of S. cerevisiae var. bayanus, and fermentation was carried out at room temperature (32 ± 2°C) for 6 days. Racking of wine was carried out when total soluble sugars reached 2 to 3°Brix.

Two or three more rackings were done at 15-day intervals to remove any sediment deposited in the wine. After racking, the wine was clarified with the addition of 0.04% bentonite and analyzed. Sodium metabisulfite (100 mg/mL) was added as a preservative before bottling. A general flowchart for cashew wine production is shown in Figure 13.1.

Despite the high level of tannin content, cashew apples could be processed into beverages owing to their fleshy pulp, soft peel, lack of seeds, high sugar concentration, and strong exotic flavor.

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Other Processes Using Cashew Apple Juice as Substrate

The use of agricultural excesses as a substrate in industrial fermentations became an interesting alternative to reduce production costs and to reduce negative environmental impact caused by the disposal of these products. Mannitol is sugar alcohol applied as a sweetener.

Heterofermentative lactic acid bacteria, such as Leuconostoc mesenteroides sp. are able to produce mannitol from fructose. Because the carbohydrates of cashew apple juice are glucose and fructose, Fontes et al. (2009) studied the use of cashew apple juice as a substrate for mannitol production.

The best results were obtained by applying only cashew apple juice as a substrate, containing 50 g/L of total reducing sugar (28 g/L of fructose), yielding 18 g/L hour–1 of mannitol with 67% of fructose conversion into mannitol and productivity of 1.8 g/L hour–1.

The use of cashew apple juice as a low-cost substrate for Lactobacillus casei B-442 cultivation and lactic acid production was studied by Silveira et al. (2010). Lactic acid is applied in the food industry as a preservative and L. casei is a probiotic bacteria.

Because of the low protein content of cashew apple juice, ammonium sulfate was used as the only exogenous nitrogen source, replacing the use of yeast extract, which is a more expensive nitrogen source for industrial applications. The effect of cashew apple juice reducing sugars, ammonium sulfate concentration, the fermentation pH, and temperature on biomass formation, lactic acid production, and productivity were evaluated.

Last word

The highest productivity (2.36 g/L hour–1) was obtained by applying 50 g/L of reducing sugar from the cashew apple juice supplemented with 6 g/L of ammonium sulfate. The process yield was approximately 95% when fermentation was carried out at 37°C with pH-controlled at 6.5 using sodium hydroxide (120 g/L). The biomass produced can be used as a supplement in the food industry due to its probiotic effects.

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