Utilization of endogenous amylases and Pectinex enzymes for efficient extraction of sweetpotato Juice

Abstract

Sweetpotato (Ipomoea batatas (L.) Lam) is one of the most important, versatile and underexploited crops in Kenya. Lack of organized marketing, limited consumer interest and low level of value addition are major factor that contribute to this unfortunate scenario. Processing of non-alcoholic beverages and fuel ethanol are feasible options of commercializing the roots, but lack of an efficient and low cost method of extracting juice has been a major constraint especially in third world countries. The most efficient method of extracting sweetpotato juice available currently involves the use of expensive commercial amylases and starch debranching enzymes. The overall objective of this study was therefore to develop an efficient and low cost method of extracting sweetpotato juice using a combination of endogenous amylolytic enzymes and pectinex 3XL enzyme. The specific objectives of the study were; to determine the effect of sweetpotato variety, temperature and curing duration on endogenous a-amylase and f}- amylase activities in three sweetpotato varieties; to study the effect of endogenous a-amylase activity on starch hydrolysis in sweetpotato purees incubated at 60, 65, 70, 75°C for 180 minutes; to determine the effect of pectinex 3XL enzyme on viscosity and yield of juice from saccharified sweetpotato purees and to characterize three local sweetpotato root varieties in terms of yield and quality of juice extracted. To study the effect of temperature, curing duration and variety on amylolytic activities in sweetpotato roots, a 3x3x3 factorial experiment in a completely randomized design was used. The effects of temperature and curing duration on endogenous a-amylase activity were found to be highly significant while varietal effect was not. The first order interactions between; temperature and time, variety and temperature and second level interactions between the three factors were also found significant. Endogenous f}-amylaseactivity in sweetpotato roots did not change in a consistent fashion; decreasing in Muibai and Gikanda yellow sweetpotato while remaining the same in Gikanda white. A 4x7 factorial experiment in a randomized complete block design was used to investigate the effect of endogenous a-amylase activity on starch hydrolysis in Muibai sweetpotato purees from roots cured for between 1-6 days at 35°C. ANOV A of the results showed that temperature and a-amylase enzyme activities significantly influenced maltose formation in the purees. The endogenous amylolytic enzymes were able to convert more than 75% of

starch in the sweetpotato purees to sugar, which demonstrates that the enzymes could be used for improving the efficiency and reduce the cost of extracting sweetpotato juice. A randomized complete block design was used to study the effect of pectinex 3XL enzyme on the viscosity and yield of juice from saccharified sweetpotato purees. ANOV A of the results showed that the effect of pectinex enzyme on puree viscosity and juice yields was highly significant. The yield of juice increased from 30-500.10 when no enzyme was used to about 80% as little as 20Omg/Kg pectinex enzyme was added to the puree. Results of proximate composition analysis of sweetpotato root and juice showed that JOOstof the solids present in the roots were dissolved in the juices and that the sugars contents of juices (14%) was sufficient for fermentation to alcohol. Therefore, the objectives of the study were achieved which means that commercial exploitation of sweetpotato roots for production of low cost non-alcoholic beverages could be viable options even in less technologicalJy advanced countries such as Kenya.