title: Compromised Lactobacillus helveticus starter activity in the presence of facultative heterofermentative Lactobacillus casei DPC6987 results in atypical eye formation in Swiss-type cheese.
abstract: Nonstarter lactic acid bacteria are commonly implicated in undesirable gas formation in several varieties, including Cheddar, Dutch-, and Swiss-type cheeses, primarily due to their ability to ferment a wide variety of substrates. This effect can be magnified due to factors that detrimentally affect the composition or activity of starter bacteria, resulting in the presence of greater than normal amounts of fermentable carbohydrates and citrate. The objective of this study was to determine the potential for a facultatively heterofermentative Lactobacillus (Lactobacillus casei DPC6987) isolated from a cheese plant environment to promote gas defects in the event of compromised starter activity. A Swiss-type cheese was manufactured, at pilot scale and in triplicate, containing a typical starter culture (Streptococcus thermophilus and Lactobacillus helveticus) together with propionic acid bacteria. Lactobacillus helveticus populations were omitted in certain vats to mimic starter failure. Lactobacillus casei DPC6987 was added to each experimental vat at 4 log cfu/g. Cheese compositional analysis and X-ray computed tomography revealed that the failure of starter bacteria, in this case L. helveticus, coupled with the presence of a faculatively heterofermentative Lactobacillus (L. casei) led to excessive eye formation during ripening. The availability of excess amounts of lactose, galactose, and citrate during the initial ripening stages likely provided the heterofermentative L. casei with sufficient substrates for gas formation. The accrual of these fermentable substrates was notable in cheeses lacking the L. helveticus starter population. The results of this study are commercially relevant, as they demonstrate the importance of viability of starter populations and the control of specific nonstarter lactic acid bacteria to ensure appropriate eye formation in Swiss-type cheese.
authors.affiliation: Teagasc Food Research Centre, Moorepark, Fermoy, P61 C996 Co. Cork, Ireland; School of Food and Nutritional Sciences, University College Cork, College Road, Cork T12 Y337, Ireland.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: O'Sullivan
authors.affiliation: School of Food and Nutritional Sciences, University College Cork, College Road, Cork T12 Y337, Ireland.
authors.forename: Paul L H
authors.initials: PLH
authors.lastname: McSweeney
authors.affiliation: Teagasc Food Research Centre, Moorepark, Fermoy, P61 C996 Co. Cork, Ireland; APC Microbiome Institute, University College Cork, College Road, Cork T12 YT20, Ireland. Electronic address: Paul.Cotter@teagasc.ie.
authors.forename: Paul D
authors.initials: PD
authors.lastname: Cotter
authors.affiliation: Teagasc Food Research Centre, Moorepark, Fermoy, P61 C996 Co. Cork, Ireland. Electronic address: Linda.Giblin@teagasc.ie.
authors.forename: Linda
authors.initials: L
authors.lastname: Giblin
authors.affiliation: Teagasc Food Research Centre, Moorepark, Fermoy, P61 C996 Co. Cork, Ireland.
authors.forename: Jeremiah J
authors.initials: JJ
authors.lastname: Sheehan
mesh_terms: D000818:Animals; D002611:Cheese / Q000032:analysis / Q000382:microbiology* / Q000592:standards*; D005285:Fermentation; D005516:Food Microbiology; D007780:Lacticaseibacillus casei / Q000502:physiology*; D052198:Lactobacillus helveticus / Q000502:physiology*; D048249:Streptococcus thermophilus / Q000502:physiology
keywords: Swiss-type cheese; X-ray computed tomography; gas defects; heterofermentative lactobacilli