Optimization and physicochemical characterization of juice extraction from Opuntia ficus-indica fruit peel and its application in vinegar production

Harnessing cactus pear ( Opuntia ficus-indica ) fruit peel as bio-resource underscores the power of biotechnology to maximize the industrial value of underutilized crops. The valorization of cactus pear fruit peel for vinegar production has rarely been investigated. Despite its abundant production, much of the unused fruit and its peel are discarded, which causes environmental pollution. The peel contains arabinogalactan and different fractions of pectin type polysaccharides, which could be difficult to utilize it for juicing and then converting it into wine and vinegar. This study optimized the shear homogenization of cactus pear peel to create a substrate for vinegar production via a two-stage process: alcoholic fermentation using Saccharomyces species followed by acetic oxidation using Acetobacter species . Employing response surface methodology (RSM) coupled with central composite rotatable design (CCRD), the shear homogenization input factors were optimized to develop a peel juice substrate. The optimal conditions (50 °C, 4.92 min, and 21,500 rpm) yielded a substrate with 2.87 ± 1.01 (% citric acid) titratable acidity (TA), 6.1 ± 0.4 °Brix of total soluble solids (TSS), and 4.7 ± 0.113 mg/100 g of ascorbic acid (vitamin C). Wine produced using this substrate yielded promising results for vinegar production, achieving a vinegar fermentation yield of 46.3%, acetic acid concentration of 8.5% (w/v), and ethanol concentration of 0.83% (w/v). Other physicochemical qualities were found to be promising.