Impact of Nutrient Supplementation of Synthetic Grape Juice on Growth of Pediococcus spp. Post-Alcoholic Fermentation
Megan Wade,* James Osborne, and Charles Edwards
*Washington State University, 100 Dairy Road, School of Food Science, Pullman, WA 99164 (firstname.lastname@example.org)
Commonly isolated from red wines, recent proliferations of Pediococcus spp. may be due to excessive supplementation of musts with nutrients not consumed during alcoholic fermentation. To assess the impact of excessive supplementation, synthetic grape juices were prepared containing low (60 mg N/L) or high (600 mg N/L) yeast assimilable nitrogen (YAN) and fermented by Saccharomyces cerevisiae D254. After 14 days, wines were sterile-filtered and inoculated with different strains of P. parvulus, P. damnosus, P. inopinatus, or P. pentosaceus. Concentrations of amino acids, titratable/volatile acidities, and ethanol were measured before and after inoculation using standardized methods. Of the six species/strains examined, only two (P. parvulus OW-1 and P. damnosus OW-2) exhibited logarithmic growth in the low-YAN wines, while none grew in high-YAN wines. Growth in the low-YAN wines suggests increased risks of Pediococcus spoilage in wines undergoing stuck alcoholic fermentations. However, all strains inoculated into the high-YAN treatments declined to undetectable populations shortly after inoculation. Wines that did not support bacterial growth were sterile-filtered and redistributed into 10 mL test tubes prior to supplementation with peptone, yeast extract, liver extract, Tween 80, cysteine, asparagine, manganese sulfate, biotin, or calcium pantothenate. After re-inoculation of Pediococcus spp., growth was monitored for an additional 24 days. The addition of yeast extract greatly improved growth of all six strains, while peptone improved growth for five of the six. Here, logarithmic growth was observed in low-YAN wines, where populations reached >106 cfu/mL, suggesting the presence of important growth factor(s) for Pediococcus in yeast extract and peptone. As further supplementation of high-YAN wines did not affect bacterial growth, the higher ethanol concentrations present may have affected the nutrient requirements of Pediococcus.
Funding Support: Northwest Center for Small Fruits Research