Microbial dynamics in barley grain stored under controlled atmosphere

Abstract

Barley of 2 moisture contents, 20–23% and 26–28%, was stored airtight for 2 separate seasons in 2 full-scale silos, and for 3 separate seasons in 12–16 pilot silos (1.25 m 3). The microbial dynamics were studied, using colony-forming units (CFU) of microorganisms, the proportion of internally-invaded kernels and ATP content. The ATP content was a good measure of the microbial activity, which decreased after loading and was very low during the winter period. Field-associated moulds and yeasts decreased in numbers of CFU and in the amount of invaded kernels. Fusarium species survived more satisfactorily than most field fungi. The temperature rise in spring caused an increase in ATP content, as a result of extensive growth of yeast of the genera Hansenula and Candida. This activity started earlier in the high-moisture grain (March). In May, a significant increase in CFU of Penicillium was observed and, during May to July, in many silos, all kernels were invaded, mostly by P. roqueforti. In an attempt to increase the time of safe storage, some technical improvements and gaseous and liquid chemical additives were tested. Attachment of “lungs” to the silos, and addition of organic acids or gases (CO 2, N 2, NH 3) to the grain, increased the safe storage time by one to several months. The aerobic storage stability of rolled barley taken in July from the full-scale silos was tested. The rapid deterioration following unloading limited the aerobic storage stability to a few days.