SORPTION CHARACTERISTICS AND STORAGE STABILITY OF FERMENTED AND DRIED LOCUST BEAN (PARKIA BIGLOBOSA) SEED

Abstract

Locust bean (Parkia biglobosa) is a well cherished traditional seasoning agent with high export potential, but has limited information on sorption characteristics and storage stability. This study is aimed at determining the sorption characteristics and storage stability of Locust bean seeds. The seeds, obtained from Olode village, Osun State were cleaned, destoned, boiled and fermented following traditional method to produce iru condiment. The iru produced was dried in hot air oven at 75oC for 12 hours to a moisture content of less than 10%. The dried iru was divided into two portions, a portion was used for sorption isotherm study and the second portion was packaged in three different packaging materials and used for storage stability study for a period of twelve weeks. Three different packaging materials used in carrying out the storage stability study include: low density polythene (LDPE), transparent plastic packages, and aluminium foil. The samples were kept at ambient temperature of 29+1o C for twelve weeks. At intervals of four weeks samples were drawn from these three packages to determine their physicochemical and microbiological properties. Sensory evaluation was done for the remaining stored sample at the end of twelve weeks storage period. Data obtained were subjected to statistical analysis (ANOVA). The physicochemical result showed that the variations in the moisture content, % Free fatty acid and Peroxide values were not significant (p < 0.05), while the pH and thiobarbituric acid (TBA) values showed significant differences. pH values at the fourth week were found to be significantly lower than those of weeks 8 and 12 weeks, while the TBA value for Iru stored in polythene bag was significantly lower than from those in plastic and aluminium foil wrappers. Result from sensory evaluation showed that iru stored in polythene packaging ranked better than the other samples. The result of microbiological analysis showed that mould and yeast together with coliform bacteria were absent all through the twelve weeks period. Total viable count increased from 4.6x106 to 7.1x106 cfu/g. Bacillus cereus colonies having typical rough dry appearance ranged between 3.4x106-5.5x106 cfu/g, and positive Staphylococcus aureus colonies with black shining convex appearance surrounded by a clear zone were obtained. Monolayer moisture values of 4.1 and 4.2 g/100g at 30 oC and 40 oC respectively were recorded from sorption isotherm studies. These values were indicative of levels of hydration at which the keeping qualities of dried iru will be best maintained. This study showed that drying iru condiment to moisture content of less than 10% immediately after fermentation enhanced its commercial acceptance, and storing it at relative humidity of less than 50%, in polythene packaging (that prevented interaction with surrounding environment), is a simple and practical way of , extending its shelve life