Vinegar Production from Pineapple Waste by Semi-Solid State Fermentation

Using pineapple waste that is a by-product of the pineapple processing industry and consists of residual pulp, peels and skin as fermentation substrate, semi-solid state fermentation in a twice sugar supplement mode was carried out for vinegar production. Wine yeast and acetobacter powder AS 1.01 were inoculated for alcoholic and acetic acid fermentation, respectively. Process conditions for pineapple waste fermentation were optimized in order to achieve higher acid production in a shorter time. Amount of inoculated wine yeast of 0.3%, fermentation temperature of 22 ℃, sugar content of 16 °Brix, pH value of 3.5 and fermentation time of 6 days were found optimum for alcoholic fermentation, and the optimum conditions for acetic acid fermentation were found to be: amount of added glucose 2%, initial alcohol concentration 8%, fermentation temperature 29 ℃, amount of inoculated acetobacter powder AS 1.01 of 0.09% and fermentation time ranging from 3 to 4 days. Under these optimum conditions, the acid production (calculated as acetic acid) was up to 6.78 g/100 g of fermented pineapple waste, and the conversion ratio of acetic acid was 82.5%. After soaking, filtration and aging for 1-2 months, the total acid content in the final vinegar product was 3.672 g/100 mL, which had golden yellow color, both vinegar and pineapple flavor and a soft and refreshing taste, and was clear and transparent. Semi-solid state fermentation gave a higher total acid production in a shorter time in comparison with liquid-state fermentation.