Towards the development of a starter culture for improvement of grain storage through biopreservation

Sammanfattning: In temperate countries such as Sweden, where much rain falls during the harvest period, problems can occur later during preservation of feed grains because of too high water contents in the grains. Drying by heated air is the most commonly used operation in Sweden to reduce water content in grains. If airtight storage is used instead, energy and money can be saved, as airtight storage only consumes 2 % of energy needed for heated air drying. Through biopreservation, where added microorganisms enhance the stability of the cereals in the airtight storage system by preventing mould growth, a more stable preservation can be obtained. To achieve a safe storage, insensitive to air leakage, the starter culture must work properly independently of the moisture content in the grains. To expand the acceptable region of moisture content, combinations of several organisms can be used as a starter culture. A mixture of the yeast Pichia anomala J121, a lactic acid bacteria (LAB) and a propionic acid bacteria (PAB) may be an ideal starter culture, as the yeast can work in relative dry grains and the bacteria in more moist grains. However, having several organisms in the starter culture can cause problems. For example, P. anomala J121 can metabolize lactic acid produced by LAB, as oxygen enters the system in the moist grains. This results in an increase in pH, allowing detrimental organisms to grow. The ability of different LAB and PAB isolates to inhibit P. anomala J121 was therefore investigated. Slight inhibition of the yeast was only observed for Propionibacterium freundenreichii subsp. shermanii MP5, P. freundenreichii MP23 and P. thoenii MP11. To work as a starter culture, the microorganisms must be able to grow and produce organic acids and/or other antifungal compounds. Therefore, we investigated the ability of different combinations of PAB, Lactobacillus plantarum MiLAB393(pLV100) and P. anomala J121 to inhibit the mould species Penicillium roqueforti J5 at moisture contents of 25 % and 33 % in a mini silo system. The mould growth was mainly affected by P. anomala J121. Since the yeast seemed to have lower ability to grow at moisture content of 33 %, a starter culture with several organisms seems to be preferred. Of the PAB investigated in the study, Propionibacteria thoenii MP11 is the most suitable PAB in a starter culture, due to its ability to grow and produce organic acids. However, additional LAB and PAB need to be characterized and tested in different combinations.