Fungi and bacteria associated with stored grain corn in self-regulated atmospheres

FACUNDO MARCOS VALLE; CLAUDIA CASTELLARI; RICARDO BARTOSIK

Mar del Plata

Congreso; X Congreso Argentino de Microbiología General SAMIGE; 2014

Sociedad Argentina de Microbiología General

Maize is an important crop that is used worldwide as human food, as a raw material for starch and ethanol production, and as animal feed. Because of its relatively high moisture and starch contents maize is very susceptible to biological degradation. The microbial degradation of grains during storage depends principally on a combination of three factors: temperature, grain moisture content (m.c.) and O2 level. Furthermore, these microorganisms are responsible for the alteration of important germinative properties of seeds and, in the case of moulds, for the potential formation of mycotoxins. The purpose of the present study was to characterize the microbial population present in maize kernels in self-regulated modified atmospheres during hermetic storage. Corn samples with 14.5, 16.5 and 18.5% m.c., stored in hermetically sealed containers at 15, 25 and 35ºC, were analyzed at the beginning of the hermetic storage period (21% O2) and when complete depletion of O2 occurred due to aerobic respiration. The concentration of O2 was determined with a Shimadzu GC-17A gas chromatograph equipped with a flame ionization detector. Each corn sample was suspended in sterile peptone water and plated in plate count agar for isolating the total aerobic bacteria, and for yeasts and molds on potato dextrose agar. Successive peals from colonies were perfomed and these presented different morphology. Pure isolates were identified using conventional taxonomy techniques based on morphological and biochemical characteristics. The higher the m.c. the shorter the time it took for the O2 to be consumed during the aerobic respiration. At m.c. constant, O2 was consumed faster at higher storage temperatures. Most of the fungi species isolated from corn grain samples under different condition of hermetic storage belonged to the genus Penicillium, including P. citrinum, P. funiculosum, P. restrictum, P. nalgiovense, P. olsonii, P. raistrickii, P. oxalicum, P. islandicum and P. funiculosum. Also were identified species of genera Eurotium, Aspergillus, Fusarium and Acremonium, in this order of importance. The yeasts (Debaryomyces hansenii, Candida parapsilosis and Rhodotorula mucilaginosa) were the most frequent isolated group (58.33%), principally in high m.c. of grains and anaerobic conditions. The bacteria strains identified were: Alcalígenes sp., Corynebacterium sp., Lactobacillus sp., Acetobacter sp., Bacillus sp., Streptococcus sp., Actinobacillus sp. and Enterobacterias. Most bacterial isolates identified correspond to fermentative bacilli that can grow in an environment without O2. The self-regulated modified atmospheres, by lowering the level of O2 , limit the amount of species of microorganisms that can alter the quality of the stored grain. Therefore, the hermetic storage of the grains has advantages related to reducing the microbial activity and preserving the quality of grain in comparison with conventional storage practices, specially for wet grains.