APPLICATION OF LACTIC ACID IN PRESERVATION OF NINH THUAN GREEN GRAPES NH01-48

Abstract

Ninh Thuan green grapes NH01-48 is popularly cultured in Ninh Thuan province. However, due to the lack of preservation technology and/or facility, Ninh Thuan grapes are transported to and consumed in other areas of the country in a limited volume. This study aimed to assess application of lactic acid in treatment of Ninh Thuan grapes for preservation. Effect of lactic acid on grapes with or without challenging microorganisms was examined. Green grapes NH01-48 was washed with sterile water, and then dried on air. Grapes were challenged with a cocktail of microorganisms previously isolated from Ninh Thuan grapes, including four bacterial strains (Bacillus cereus, Pseudomonas oryzihabitans, Citrobacter sp., and Flavobacterium sp.), three yeast strains (Wickerhamomces anomalus, Hanseniaspora opuntiae, Debaryomyces nepalensis) and one fungus Penicillium sp. at 5 × 104 CFU/ml. Then grapes were treated with 3 % lactic acid solution for 5 min (soaking) prior to be packed in plastic bags with punched hole of 3 mm diameter, distance between holes is 3 cm and preserved in refrigeration condition at 4 ± 0.5 oC. Grapes without challenging microorganisms/without acid pretreatment/without challenging microorganisms but treated with acid were used for comparison. Samples were taken every 5th day until 30 days. Color, hardness, total dry matter, titration acidity, and total microorganism count were measured. Results showed that when applied treatment of lactic acid on grape with and without challenging microorganisms, the change in grapes’ hardness, color, dry matter and titration acidity was minimized, demonstrating positive activity of lactic acid on grape physicochemical characteristics. Samples without lactic acid treatment were spoiled after 15-20 days of preservation, whereas the ones with acid treatment can be last for at least 30 days. Moreover, number of total microorganisms count after 30 days of preservation were acceptable in samples with lactic acid treatment (ca. 103 CFU/g). Therefore, lactic acid can be potential for application in grapes preservation. The combined effect with other preservation techniques needs to be further studied.