Influence of different preservation techniques and packaging materials on the activity of stored Kepi grains

[摘要] ENGLISH ABSTRACT:Kepi is a refreshing, fermented dairy beverage that has been consumed forcenturies and is traditionally made by incubating Kepi grains in milk. The Kepigrain is a complex starter culture consisting of a variety of lactic acid bacteria andyeasts. The successful marketing of the grains requires the effective preservationof the microbes present in the grains as well as an appropriate packaging that willretain the acidification activity of the preserved grains over an extended period oftime. The aim of this study was to evaluate different preservation techniques andpackaging materials in terms of their respective abilities to retain grain viability andactivity over an extended storage period. Four different preservation techniques(freezing at -18°C, refrigeration at 4°C, air-drying and Iyophilisation) and threepackaging materials including a low density polyethylene film (LOPE), an orientedpolyester film (OPET) and a metallised oriented polyester film (MOPET), wereevaluated.Activity tests were used to evaluate the impact of the preservationtechniques in terms of the retainment of the acidification activity of the preservedgrains, and the storage potential of the preserved and packaged grains. Theactivity tests included changes in pH, %TA, lactic acid production and lactose andvolatile compound content over an 18 h fermentation period. In addition, themicrobial viability of the packaged Iyophilised grains after two months of storage,was also investigated. Frozen and refrigerated grains showed the best retainmentof the acidification activity over a 10-month storage period. Air-drying andIyophilisation showed a good retention of the activity up to three months ofstorage, but the application of these techniques both resulted in a retarded initialacidification activity. After 10 months of storage, the air-dried and Iyophilisedgrains showed only a low acidification activity. No volatile compounds could bedetected during the course of the fermentation period, due to the relative shortfermentation period of 18 h.Overall, the best retainment of the fermentation activity was given by theLOPE and the OPET packaging films. However, the storage period had aconsiderable influence on the retention of the activity of the packaged Iyophilisedgrains. The viability study of the Iyophilised packaged Kepi grains after twomonths of storage showed leuconostocs and lactobacilli to be the prevalentmicrobes in the grains. Low microbial counts were obtained from the lactococciselectingmedium for all three of the differently packaged Kepi grains, whereas nogrowth was observed on the media that selected for the propionibacteria andyeasts. The OPET packaging film provided the best preservation of the microbialcomposition.It was, therefore, concluded that all four preservation techniques would besuitable for the preservation of Kepi grains and the subsequent storage at roomtemperature for three months. However, for storage periods of 10 months orlonger the use of freezing and refrigeration are recommended as most suitablepreservation techniques. All three of the packaging materials proved to besuitable for the packaging and storage of the Iyophilised Kepi grains for periods ofup to one month. However, for storage periods of two months or longer, the use ofthe OPET film for the packaging and retainment of the acidification activity of theIyophilised grains, can be recommended.

[发布机构] Stellenbosch University