Microbial Activation of Wooden Vats Used for Traditional Cheese Production and Evolution of Neoformed Biofilms

Abstract

Three Lactococcus lactis subsp. cremoris strains were used to develop ad hoc biofilms on the surfaces of virgin wooden vats used for cheese production. Two vats (TZ) were tested under controlled conditions (pilot plant), and two vats (TA) were tested under uncontrolled conditions (industrial plant). In each plant, one vat (TA1 and TZ1) was used for the control, traditional production of PDO Vastedda della Valle del Belìce (Vastedda) cheese, and one (TA2 and TZ2) was used for experimental production performed after lactococcal biofilm activation and the daily addition of a natural whey starter culture (NWSC). Microbiological and scanning electron microscopy analyses showed differences in terms of microbial levels and composition of the neoformed biofilms. The levels of the microbial groups investigated during cheese production showed significant differences between the control trials and between the control and experimental trials, but the differences were not particularly marked between the TA2 and TZ2 productions, which showed the largest numbers of mesophilic lactic acid bacterium (LAB) cocci. LAB populations were characterized phenotypically and genotypically, and 44 dominant strains belonging to 10 species were identified. Direct comparison of the polymorphic profiles of the LAB collected during cheese making showed that the addition of the NWSC reduced their biodiversity. Sensory evaluation showed that the microbial activation of the wooden vats with the multistrain Lactococcus culture generated cheeses with sensory attributes comparable to those of commercial cheese. Thus, neoformed biofilms enable a reduction of microbial variability and stabilize the sensorial attributes of Vastedda cheese.

FIG 1

Scanning electron microscopy observations of wooden splinters. (A) Virgin vat after 30 days of hot water treatment. (B) Vat TZ1 after overnight contact with whey obtained from a traditional Vastedda cheese made with raw milk. (C) Vat TZ2 after overnight contact with the NWSC developed with the multistrain Lactococcus culture.

FIG 2

Dendrogram obtained with combined RAPD-PCR patterns generated with three primers for LAB strains from vats and samples collected during cheese productions. The line at the top indicates percentages of similarity. Abbreviations: E., Enterococcus; Lb., Lactobacillus; Lc., Lactococcus; Ln., Leuconostoc; P., Pediococcus; S., Streptococcus; TA1, control production at the dairy factory; TZ1, control production at the dairy pilot plant; TA2, experimental production at the dairy factory; TZ2, experimental production at the dairy pilot plant; VS, vat surfaces; BMAR, bulk milk after resting; C, curds; W, whey; AC, acidified curds; ChT₀, cheese at T₀; ChT₁₅, cheese at 15 days.