Department of Microbiology, Stellenbosch University, Stellenbosch, South Africa.
Folia Microbiol (Praha). 2021 Jun;66(3):341-354. doi: 10.1007/s12223-021-00850-8. Epub 2021 Jan 20.
It is estimated that more than 20% of processed apples and grapes are discarded as waste, which is dominated by pomace rich in malic acid that could be converted to high-value organic acids or other chemicals. A total of 98 yeast strains isolated from apple, grape, and plum wastes were evaluated for their ability to degrade malic acid relative to known yeast strains. Most (94%) of the new isolates degraded malic acid efficiently (> 50%) in the presence and absence of exogenous glucose, whereas only 14% of the known strains could do so, thus confirming the value of exploring (and exploiting) natural biodiversity. The best candidates were evaluated in synthetic media for their ability to convert malic acid to other valuable products under aerobic and oxygen-limited conditions, with two strains that produced ethanol and acetic acid as potential biorefinery products during aerobic cultivations and oxygen-limited fermentations on sterilized apple and grape pomace. Noteworthy was the identification of a Saccharomyces cerevisiae strain that is more efficient in degrading malic acid than other members of the species. This natural strain could be of value in the wine-making industry that often requires pH corrections due to excess malic acid.
据估计，超过 20%的加工苹果和葡萄被当作废物丢弃，其中主要是富含苹果酸的果渣，可转化为高价值的有机酸或其他化学品。从苹果、葡萄和李子废物中总共分离出 98 株酵母菌株，评估其相对于已知酵母菌株降解苹果酸的能力。大多数（94%）新分离株在存在和不存在外源葡萄糖的情况下都能有效地（>50%）降解苹果酸，而只有 14%的已知菌株能够做到这一点，从而证实了探索（和利用）自然生物多样性的价值。对最佳候选菌株在合成培养基中的性能进行了评估，以考察它们在有氧和缺氧条件下将苹果酸转化为其他有价值产品的能力，其中两株在有氧培养和对灭菌的苹果和葡萄渣进行缺氧发酵时产生了乙醇和乙酸，可作为潜在的生物精炼产品。值得注意的是，鉴定出一株比其他种属成员更有效地降解苹果酸的酿酒酵母菌株。这种天然菌株可能对葡萄酒酿造行业有价值，因为该行业由于苹果酸过量，通常需要进行 pH 值校正。
