Lihua Fan

Vineyards support highly diverse communities of native yeasts, but only a small proportion are fermentative ascomycetes capable of alcoholic fermentation. Many non‐fermentative species are also present, including a range of metabolically active basidiomycete yeasts that can influence wine aromatic profiles, especially in the early stages of fermentation. In some cases, basidiomycete yeasts, such as Filobasidium , Rhodotorula , Sporobolomyces , and Vishniacozyma , are more abundant and diverse than ascomycete yeasts in grape musts, with some persisting throughout fermentation. As the existing information on the role of basidiomycete yeasts in winemaking is fragmented, we synthesize the records of these yeasts in association with wine grapes and musts, as well as the research on their potential applications in winemaking. Basidiomycete yeasts are gaining attention for their unique biochemical contributions to wine flavor, influencing sensory attributes through the production of metabolites such as acids, higher alcohols, aldehydes, ketones, esters, and glycerol, as well as by their enzymatic activities and by the production or utilization of resources used by fermentative yeasts. Basidiomycete yeasts play especially important roles in shaping spontaneously fermented wines (which rely solely on the yeasts present on the grapes) and have the potential to help produce wines with increased aromatic complexity.

Societal Impact Statement: Climate warming and demand for fuller‐bodied wines has resulted in increased grape sugar contents and, therefore, increased alcohol in wines. Concurrently, there are increased warnings about the health risks of alcohol, and consumers seek low‐alcohol options as part of a healthy lifestyle. High alcohol levels can also impact the flavor balance of wines, resulting in economic losses. However, exploration of native vineyard yeasts shows that fermentation with novel species can result in both alcohol reduction and improved wine flavor. Our findings show that native yeasts have the potential to bring the North American cool‐climate wine industry into a healthier future.Summary: There is recent interest in developing wines fermented with non‐traditional yeasts that reflect the microbial terroir of the grape‐growing region. These native yeasts inhabit grape skins and can produce wines with distinctive flavor profiles, and when used in concert with traditional wine yeast, the risk of incomplete fermentation is minimized. Non‐traditional yeasts can also produce wines with relatively low alcohol content, an attractive characteristic given the health and societal issues associated with overconsumption. Yeasts isolated from L'Acadie and Pinot Noir grapes grown at Nova Scotia vineyards were identified by DNA sequencing and characterized regarding fermentative properties. Promising isolates of Saccharomyces uvarum, Hanseniaspora uvarum, Wickerhamomyces anomalus, and Zygotorulaspora florentina were selected for mixed and sequential fermentations with Saccharomyces cerevisiae based on their ethanol and SO₂ tolerance, β‐glucosidase activity, and low H₂S production. The resulting wines were evaluated for sensory properties by 15 experienced panelists. Alcohol levels of many of the fermentations that included non‐traditional yeasts were significantly lower than those made with traditional yeast alone, while fructose was higher, and total phenolic contents were similar. Experienced panelists also found that these fermentations resulted in wines with novel fruit and floral attributes. Our results demonstrate that native yeasts from cool‐climate wine regions can be used in concert with traditional wine yeast to produce novel, lower alcohol wines with a low risk of fermentation failure. This unlocks the potential of naturally occurring yeasts from these vineyards to create wines with flavor profiles that reflect the local wine‐making regions.

Canada is a leading producer of wild lowbush blueberries, most of which are mechanically harvested, washed, individually quick frozen (IQF), and bulk packaged. Still, some berries are harvested by more gentle methods and sold as fresh-packed products. These berries do not undergo a wash step, nor are subjected to antimicrobial treatments. The purpose of this study was to conduct a microbiological survey of berries harvested in the province of Nova Scotia to assess their potential for harborage of bacterial foodborne pathogens. A combination of standardized plate count methods and 3M-Petrifilm protocols were used to enumerate total aerobic mesophilic bacteria (APC), yeasts and molds (YMC), coliforms, and generic E. coli, the latter being an indicator of fecal contamination. Overall, APC and YMC levels were 1.2 and 0.5 log greater, respectively, for berries collected early in the harvest season versus those acquired late season and varied significantly (p < 0.05) between farm (location) and harvest practices used. Berries harvested by our team using sanitized hand rakes (SH) had consistently lower APC and YMC levels than those harvested by farm crews. Yet, when gentle harvesting (GH) methods (hand-raking, walk-behind or modified mechanical harvesters) were employed on farms, lower numbers were generally observed compared to berries harvested by traditional tractor-mounted mechanized harvesters (MH). The presence of coliforms (and their levels) was also impacted by the harvest method, with detection rates of ~29%, 73%, and 92% in SH, GH, and MH samples, respectively. Mean counts were < 2.5 log₁₀ CFU/g for both SH and GH berries, but significantly higher (p < 0.05) on MH berries (3.6 log₁₀ CFU/g). Although ~56% of all berry samples collected (n = 350) contained coliforms, only 12 were positive for E. coli, 9 of which were MH samples. Only the latter had numbers > 2 log₁₀ CFU/g, but none tested positive for Shiga toxin-producing serotype O157 (STEC O157) or Salmonella spp. when using internationally recognized selective enrichment and plating methods. ATP luminescence was used to assess the general hygiene of processing lines, whereby “hot spots” for microbial activity were identified, even after cleaning., Standard selective enrichment and plating methods were used for the detection of Listeria monocytogenes on 61 swab samples taken from berry totes or conveyor belts at different times during processing; 4 swabs tested positive for L. monocytogenes. However, the pathogen could not be detected by direct plating on selective agar without prior enrichment; this indicated its numbers were low. The results from this work demonstrated that alternative gentle harvest methods can reduce microbial numbers on wild blueberries. Although the frequency of fecal contamination in berry samples appeared to be low and targeted human pathogens were not detected; this represents a single study conducted over one harvest season. Therefore, it would be prudent for processors to seek effective antimicrobial technologies prior to packaging, while consumers should use caution and thoroughly wash produce before consumption. Where sporadic detection of L. monocytogenes was observed on environmental samples from the processing line, processors must ensure that effective sanitation programs are implemented to avoid potential food safety risks.

The antibacterial effect of pomegranate juice (PJ) at six concentrations (0, 10, 20, 30, 40, and 50%) against Listeria innocua and Escherichia coli was investigated in distilled water (DW) and bacterial culture broth. L. innocua and E. coli at approximately 10⁵ cfu mL⁻¹ were inoculated in PJ samples and incubated at 4, 25, and 37 °C for 0, 6, 24, and 48 h. The bacterial population and pH of culture media were measured at each removal. Results indicated that the antibacterial effect of PJ was dependent upon bacteria species, juice concentration, incubation temperature, and growth medium. Higher juice concentration and incubation temperature resulted in increased antibacterial effects. Bacterial populations were decreased more significantly in DW systems than in the culture broth, while L. innocua was more sensitive to PJ than E. coli in the DW systems. Regardless of PJ concentrations in DW systems, L. innocua, initially inoculated at approximately 10⁵ cfu mL⁻¹, was reduced to undetectable levels at 25 and 37 °C within 24 h. The growth of L. innocua and E. coli was significantly inhibited in bacterial culture broth containing ≥ 20% PJ (p < 0.001). This study provides insight into the potential application of PJ in food and beverage products for food protection.

To improve fresh‐cut produce quality and shelf life, 0.5% or 1.0% MicroGARD ^® 730 (MG) as a natural alternative to synthetic chemical preservatives, 2.5% NatureSeal ^® (NS) product (vitamin/mineral‐based blends), 0.5% MG combined with 2.5% NS, and 1% MG combined with 2.5% NS were used to treat fresh‐cut butternut squash ( Cucurbita moschata ). The 240 g samples were put into food grade bags and stored at 4 or 7 °C. Microbial population, including aerobic plate counts (APCs), yeast and molds, total coliforms, and quality parameters, including head space O ₂ /CO ₂ concentration in package, pH, soluble solids, color, and conductivity, were evaluated after 0, 3, 6, 9, 12, and 20 days of storage. Results showed that after 6 days of storage at 7 °C, APC of check and control samples reached to 2.6 × 10 ⁸ and 1.5 × 10 ⁷ CFU/g, respectively; while they were kept at 10 ⁴ CFU/g (3 to 4 log reduction) in the squash samples treated with 0.5% or 1% MG combined with NS at 7 °C. Similar results were found on squash samples stored at 4 °C for 9 days. The cut squash treated with MG combined with NS had APC ≤ 10 ⁷ CFU/g at 4 °C for about 20 days compared to 9 days in controls or 0.5% MG‐treated samples, and 12 days in 1% MG‐treated or NS‐treated samples, respectively. Considering overall quality and extended shelf life, MG combined with NS was recommended to apply to cut squashes stored at 4 °C. Practical Application: This research provided useful information and practical treatment application for developing fresh‐cut produce with good quality and extended shelf life up to 20 days at 4 °C.

Rapid methods to detect bacterial pathogens on food and strategies to control them are needed to mitigate consumer risk. This study assessed volatile emissions from whole cantaloupe melons ( Cucumis melo ) as an indicator of Listeria contamination and in response to steam vapor decontamination. Cantaloupe were inoculated with Listeria innocua , a nonpathogenic surrogate for L. monocytogenes , then exposed to 85 °C steam for 240 s (4 min) followed by rapid chilling and storage for 0, 7, 10, or 14 days at 4, 7, or 10 °C. Volatile emissions from whole melons were collected on Carbopack B/Carboxen 1000 headspace collection tubes and analyzed by gas chromatography‐mass spectroscopy following thermal desorption. Introduction of L. innocua to cantaloupe rind resulted in a reduction of aromatic compound emission. However, this response was not unique to Listeria contamination in that steam vapor treatment also reduced emission of these compounds. As well, steam vapor treatment diminished the number of viable Listeria and indigenous microflora while causing physiological injury to melon rind. Heat treatment had no significant effects on flesh firmness, color, titratable acidity, or soluble solids, but the production of typical aroma volatiles during postharvest ripening was inhibited. No unique volatile compounds were detected in Listeria contaminated melons. While changes in volatile emissions were associated with Listeria inoculation, they could not be differentiated from heat treatment effects. Results indicate that volatile emissions cannot be used as a diagnostic tool to identify Listeria contamination in whole cantaloupe melons. Practical Application: The detection of pathogen contamination on fresh produce is a continuing challenge. Using a nondestructive screening method, the presence of surrogate Listeria innocua on fresh whole cantaloupes was shown to alter the emissions of aromatic volatiles from whole cantaloupes. However, these altered emissions were not found to be unique to Listeria spp. and therefore cannot be used as a definitive indicator of Listeria contamination.

Recent bacterial illnesses and outbreaks associated with the consumption of fresh and fresh‐cut fruit and vegetables emphasize the need to supply produce that is microbiologically safe while retaining its quality and nutrient value. We assessed the capacity of aerated steam to reduce initial levels and control the posttreatment proliferation of a 4‐strain mixture of Listeria innocua , a surrogate for L. monocytogenes , and microflora native to the rind of whole cantaloupes. Studies were conducted at the pilot‐scale level by passing deliberately contaminated melons through a prototype stainless‐steel, continuous‐feed heating device. Exposure for 240 s to aerated steam heated to 85 °C achieved a mean reduction in surface‐inoculated L. innocua of 3.9 ± 0.6 log ₁₀ CFU/cm ² ( n = 3) and decreased background microorganisms (yeast, moulds, and coliforms) to undetectable levels. No significant outgrowth of surviving L. innocua or yeast and moulds was observed on heat‐treated melons during their storage at 4, 7, and 10 °C for 14 days. Treated fruit continued to respire. Although rind quality was altered, edible fleshy portions remained largely unaffected. Cantaloupe inoculated with L. innocua subsequent to its exposure to aerated steam provided a suitable environment for surrogate growth (mean 3.3 log ₁₀ increase in rind density over 10 days at 7 °C), whereas its proliferation was restricted on nonheated cantaloupe (mean 0.7 log ₁₀ increase). Steam sanitization provides an effective means for the control of pathogen and spoilage organisms, but the proliferation of surrogate organisms on heated cantaloupes raises concern regarding the impact of postprocessing contamination on consumer health risk. Practical Application: Water vapor (steam) at a high temperature can be used to sanitize the surface of fresh, whole cantaloupe melons in a continuous‐feed manner. Both Listeria bacteria and spoilage organisms are markedly reduced from initial levels and survivor outgrowth severely restricted during subsequent refrigerated storage. This approach to microorganism control is likely most applicable in situations where rinds and flesh are to be separated immediately via further processing.