Isolation and Characterization of Alpha-Amylase Producing Bacterial Isolates from Deteriorated Onion (Allium Cepa) Bulbs

Abstract

Postharvest losses due to microbial spoilage of vegetables continue to increase in developing countries. Onion (Alium cepa) bulbs and several other vegetables are highly prone to spoilage because they are composed of living tissues hence, the need for alternative uses for these vegetable wastes. This study was designed to isolate, characterize bacterial species from deteriorated onions and screen them for alpha-amylase production. Five onion bulbs were moistened with sterile distilled water and allowed to deteriorate for three weeks. Bacterial populations isolated from the deteriorated onion bulbs were cultured on Nutrient agar plates for 24hr and 48hr. The plates were sub-cultured to obtain pure cultures. Bacterial populations isolated from the deteriorated onion bulbs were screened for alpha-amylase production on nutrient agar supplemented with 1% (w/v) starch. Alpha-amylase production was determined at 37^oC for 48hr. All isolates which were positive for alpha amylase production were identified by biochemical characteristics. Isolates showing the highest zones of hydrolysis from each onion bulb were further characterized by molecular techniques. A total of twenty-seven bacterial isolates were obtained. Biochemical characterization revealed members of the Genera Pseudomonas, Bacillus and Staphylococcus. Isolate codes A3, B3, C4, D3 and E4 from Onion A, B, C, D, E showed the highest zones of hydrolysis at 23, 4, 9, 18 and 23 mm respectively. Molecular characterization revealed that all the five isolates were Pseudomonas spp. This result established that deteriorated onion bulbs plays host to a number of alpha-amylase producing bacteria which may be exploited for industrial production of alpha-amylase.