Evaluation of bioprotective starter culture and aging temperature on gas formation by Paucilactobacillus wasatchensis in Gouda cheese using computed tomography imaging

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Late gas defects caused by nonstarter lactic acid bacteria (NSLAB) present significant economic and quality challenges in semi-hard aged cheeses. Finding practical mitigation strategies to defend against gas-producing NSLAB is important to reduce the economic impact of this defect. Paucilactobacillus wasatchensis is one species of NSLAB associated with late gas defects in Cheddar; however, little is known about its behavior in other semi-hard cheeses. This study investigated the behavior of Pa. wasatchensis in Gouda cheese and explored aging temperature and the use of bioprotective (nisin-producing) cultures to mitigate gas production. Gouda cheese was produced either using conventional or nisin-producing bioprotective starter culture with and without inoculation with Pa. wasatchensis SK0033 into the cheese milk (4 log cfu/mL). All treatment combinations of starter culture and inoculation status were replicated on 2 unique production days. Wheels (n = 4) from each production were randomized for aging at 4°C, 10°C, or 15°C for up to 40 wk. Computed tomography scanning was used as a novel, nondestructive method to observe gas formation and imaging analysis was used to quantify of gas volume within cheese wheels (n = 3/cheese make) throughout aging. Microbiome analysis was performed on selected cheese wheels at the end of aging. The fourth wheel for each treatment was used for intermittent sampling for destructive testing (i.e., pH, water activity, moisture, salt). The highest volume of gas was produced by Pa. wasatchensis in cheese made with the conventional starter at aged at 15°C. Gas volume in these wheels ranged from as low as 0.02% (0.5 wk) to as high as 2.54% (39 wk), which increased over the aging period. Considerable variability in gas volume between wheels from the same cheese make was observed which aligns with industry reports of defect variability at commercial scale. Reduced aging temperature (4°C) delayed but did not prevent gas production caused by Pa. wasatchensis during aging; growth of Pa. wasatchensis at all aging temperatures was confirmed by microbiome analysis. The replacement of the conventional starter with a nisin-producing bioprotective starter effectively prevented growth and gas formation caused by Pa. wasatchensis at all aging temperatures. The presence of nisin in the cheese made with bioprotective starter was confirmed to be active against Pa. wasatchensis using the soft agar overlay method. These findings illustrated the ability of Pa. wasatchensis to cause late gas defects in Gouda and demonstrated the efficacy of a bioprotective starter culture to mitigate this defect.