, Volume 92, Issue 5, pp 455-468,
Open Access This content is freely available online to anyone, anywhere at any time.

Characterization of the fungal microflora in raw milk and specialty cheeses of the province of Quebec

Abstract

The cheese microbial ecosystem is complex, and the presence of non-starter adventitious microorganisms in milk may have an influence on the organoleptic characteristics of cheese. The aim of this study was to analyze the composition and diversity of the fungal flora of raw milk destined for cheesemaking from 19 dairy farms in Quebec and to monitor their evolution throughout ripening. Six hundred ten yeast and mold isolates were collected from raw milk and raw milk cheeses over a 9-month period. Based on the sequences of the rDNA ITS1-5.8S-ITS2 region, 67% of the raw milk isolates were yeasts, which were assigned to 37 species across 11 genera, while 33% were molds, which were assigned to 33 species across 25 genera. A semi-quantitative analysis of the yeasts and molds in the raw milk from four farms was performed over a 5-month period. The composition and diversity of the fungal microflora were totally different for each farm, each of which had a unique species profile. To determine whether adventitious yeast strains from the milk could develop in raw milk cheese, a multilocus-sequence-typing (MLST) analysis was performed on 13 Issatchenkia orientalis (syn. Pichia kudriavzevii, anamorph: Candida krusei) isolates. The same MLST genotypes were identified for strains independently isolated from raw milk and raw milk cheese from a farm processing its own milk. This study contributes to the understanding of the natural fungal microflora of raw milk and suggests that non-starter yeasts and molds can transfer from raw milk to raw milk cheese and may influence cheese ripening.

魁北克生乳及特色干酪中真菌群落的特性

摘要 干酪微生物生态系统的复杂性影响了干酪的感官特性。原料乳中外来微生物作为非发酵剂能够影响干酪的成熟。对来自魁北克牧场19个生乳样品中真菌的组成和多样性及其加工的干酪中真菌生长繁殖情况进行了分析和评价。在9个月的实验期间,从生乳及干酪中共分离出了610株酵母和霉菌。根据rDNA ITS1-5.8S-ITS2氨基酸序列分析,酵母占总菌株的67%,共有11个属,37个种。霉菌占33%,共有25个属,33个种。在五个月的实验期间,对四个牧场生乳中的酵母和霉菌进行了半定量分析,结果表明每个牧场样品间真菌群落的组成和多样性差异显著,每个牧场都有其独特的真菌菌群特性。为了分析原料生乳中外来酵母菌株是否能在干酪中生长繁殖,对13株东方伊萨酵母(库德里阿兹威氏毕赤酵母)(Pichia kudriavzevii)进行了多位点序列分型(MLST)分析。并对从来自一个牧场的生乳及其干酪中单独分离出的菌株进行了相似多位点序列分型基因的鉴定。该研究有助于了解生乳中天然真菌群,同时也说明了非发酵剂酵母和霉菌能够从原料生乳中转移到干酪中并影响干酪的成熟。