Seasonal emergence of pathogenic bacteria in salads and remedial measures
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Date
2021
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Punjab Agricultural University, Ludhiana
Abstract
Modern food systems and ready-to-eat salads represent a complex dynamic network vulnerable to foodborne infectious outbreaks difficult to trace and control. Seasonal variations further aggravate the on-going foodborne patterns posing a fundamental public health challenge. Thus, in light of rising concern, a city-wide epidemiological surveillance study for the microbiological quality of salad samples with respect to seasonal variation (monthly average temperature) was conducted during the year 2019-2021 in Ludhiana, Punjab, India. A total of (N=350) salad samples: Greek salad (n=65), Fruit salad (n=74), Chicken salad (n=61), Pasta salad (n=74) and Sprouts salad (n=76), were collected from supermarkets, local stores, and online stores and the highest prevalence was recorded for Salmonella spp. (38.0%) followed by Yersinia enterocolitica (37.4%), E. coli (36.6%), Aeromonas
hydrophila (35.4%), Staphylococcus aureus (35.4%), Listeria monocytogenes (34.0%), Klebsiella spp. (32.8%), Campylobacter spp. (30.8%), Bacillus spp. (27.6%) and Shigella spp. (26.3%), with a total of 197/350 (56.28%) bacteriologically unsafe produce. A notable seasonal trend with statistical tool was detected for Salmonella spp. (summer), Yersinia enterocolitica (winter) and Campylobacter spp. (monsoon) subjected to the red zone of concern which warrants detailed investigation. Klebsiella spp. (r=0.926), E. coli (r=0.8453) and Staphylococcus aureus (r=0.806) were found to exhibit a significant strong correlation with ambient temperature, whereas, inverse significant correlation was recorded for Yersinia spp. (r=-0.337) and Shigella spp. (r=-0.1727). Further, the shelf-life study depicted a significant difference at 4°C as compared to storage at 15°C and 37°C. The statistical test result of overall percentage of bacteriological contamination of salad samples by BIS Standard Methods and Bacteriological Food Testing Kit (BFTK) at 5% showed no significant difference accentuating an equal effectiveness of the two methods, the latter being rapid and cost-effective. Finally a promising intervention against the pathogenic microflora of salads: washing the produce with sodium hypochlorite (100ppm/5min) was found effective and the bioprocess for development of shelf stable, microbiologically safe and nutritionally enriched reproducible technology of lactic-acid fermented turmeric salad dressing (Lactic salad dressing) was optimised: [Turmeric 10%: ginger extract 7.5%: lemon juice 25%: xanthan gum 0.5%]; dilution ratio (1:1); condiment concentration (2.0%), pasteurization at 52ºC for 15 seconds and fermentation with pure culture consortia of ten established PAU lactic acid bacterial strains as starter culture (15.0%) at 37ºC for 24 hours. The microbiological and physicochemical parameters (90 days) of Lactic salad dressing were; ºBrix 1.5, titrable acidity 1.15 %, pH 2.15, total sugar 15.38 mg/100ml, reducing sugar 4.70 mg/100ml, antioxidant activity 58.11%, total polyphenols 37.12 mg GAE/100mL, total flavonoids 43.78 mg/100mL maintaining cell counts of 6.99 log CFU/mL. The fermented salad dressing is endowed with bioactive compounds of turmeric and a broad array of lactic culture metabolites, organic acids, antioxidants, polyphenols and flavonoids. The dressing when seasoned on salads (@1000mg/mL) showed high antimicrobial activity against Staphylococcus aureus MTCC3906, Listeria monocytogenes MTCC657, Klebsiella pneumoniae MTCC109, Escherichia coli MTCC443 and S. enterica serovar typhimurium MTCC 733. The current bio-invention, thus, is an economical and alternative plant based biological therapy: for replenishing gut microbiota in the era of microbial contamination and antibiotic resistance.
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Jawanda, Ishwerpreet Kaur (2021) Seasonal emergence of pathogenic bacteria in salads and remedial measures (Unpublished M.Sc. thesis). Punjab Agricultural University, Ludhiana, Punjab, India.