Control of Listeria monocytogenes in Vacuum‐Packaged Pre‐Peeled Potatoes

Abstract

Growth of Listeria monocytogenes on the surface of fresh peeled potatoes, treated with sulfite or a commercial browning inhibitor (CBI), packaged under vacuum and stored at 4, 15 and 28°C was determined. At 4°C, L. monocytogenes did not grow in all treated potatoes even after 21 days. At 15°C, L. monocytogenes grew to 7 log 10 CFU/g within 12 days in the potatoes treated with sulfite or CBI. At 28°C, L. monocytogenes population was greater than 3 log 10 CFU/g by 24 h in all samples regardless of treatment. Sulfites or a CBI appeared to provide a measure of safety in pre-peeled potatoes packaged under vacuum when kept at proper refrigeration temperatures.Key Words: Listeria monocytogenes, browning inhibitor, potatoes for inoculum preparation prior to all experiments. Preparation of inoculumInoculated BHI was incubated at 37°C for 18h. The cells were harvested by centrifugation at room temperature for 10 min at 7,700 ∞ g, the cell pellet washed twice, resuspended and diluted in sterile 0.1% peptone water (w/v) (Difco). Sample preparation and inoculationFresh, raw Russet potatoes ( 80-110g each) were obtained from a commercial potato distributor. Potatoes were abrasionpeeled for 2 min with a Vegetable Peeler (Model A1-15, Toledo Scale Co., Toledo, OH) and held under water up to 30 min prior to treatment. Potatoes received one of 4 different treatments: (1) immersion in 1.2% (w/ v) sodium bisulfite for 2 min, (2) immersion in a 2% (w/v) solution of a commercial browning inhibitor (CBI) consisting of citric acid, ascorbic acid, sodium acid pyrophosphate and L-cysteine HCl for 5 min, (3) immersion in a 2% solution of the CBI for 5 min, followed by a brief rinse with tap water (30 mL rinse/kg potatoes), or (4) untreated control. Residual sulfite levels were determined in uninoculated control samples by the Optimized Monier-Williams Method (Hillary et al., 1989).Duplicate sets of two potatoes ( 100g each) were weighed into filter stomacher bags (SFB-0410; Spiral Biotech., Bethesda, MD) and inoculated with 1 mL of an appropriate dilution of L. monocytogenes cell suspension to yield a final concentration of 1-2 log 10 CFU/g. Thereafter, the bags were manually massaged to ensure even distribution of organisms on the surface of the potatoes. The bags were placed in 17.8 ∞ 20.3 cm barrier bags (Koch Model 01 46 09, Kansas City, MO). The oxygen transmission rate (by manufacturer) of the nylon/polyethylene film was 54.2 cc/m 2 in 24h measured at 24°C and 75% relative humidity. The bags were evacuated to a negative pressure of 1000 millibars and heat sealed using a Multivac Model A300/ 16 gas packaging machine (Germany). Two replications were performed for each treatment. For each replicate experiment, two bags of each treatment were prepared for each sampling time and temperature. Controls consisted of inoculated, untreated potatoes stored under vacuum.

Effect of packaging oxygen transmission rate on the shelf life of ready‐to‐heat foods susceptible to postcontamination during refrigerated and illuminated storage

“…No effect of packaging material choice on the growth of L. monocytogenes on the potato slices or the composite meals could be detected. The finding that the potato slices did not support the growth of L. monocytogenes corresponds with findings from Juneja, who found no significant growth of L. monocytogenes on inoculated potato slices stored under refrigeration for up to 21 days. It should be noted though that in this research the slices were stored at 4°C.…”

“…Ubiquitous and persistent in food‐processing environments, it may occur in food products due to postcontamination . If the pathogen is not adequately inactivated by heating the food before consumption, this will pose a health risk to the consumer …”

Determination of 5-Log Reduction Times for Escherichia coli O157:H7, Salmonella enterica, or Listeria monocytogenes in Acidified Foods with pH 3.5 or 3.8†

“…Currently, processors must list preservatives used and their concentration on forms when filing their processes with the FDA. However, results of several studies have indicated that preservative acids, including benzoate, sorbate, and sulfite, contributed to killing pathogenic bacteria in foods (8,9,11,18). A comparative study of the relative concentrations of organic acids needed for a 5-log reduction of E. coli 0157:H 7 at pH 3.2 revealed that benzoic and sorbic acids were significantly more effective than common food acids (citric, malic, lactic, and acetic) for killing bacterial pathogens, based on equimolar protonated acid concentrations (13).…”

Conservazione degli alimenti mediante atmosfere modificate

“…Nelle patate sbucciate, inoculate con L. monocytogenes e confezionate sotto vuoto in buste a elevata barriera, a 4°C per 21 giorni non si osservava crescita, ma a 15°C il batterio arrivava a 7 log 10 /g in 12 giorni 53 . A 10°C la crescita si verificava in tutti i campioni, tranne nelle carote grattugiate.…”