Evaluation of Media for Enumerating Yeasts and Molds in Fresh and Frozen Fruit Purees

Beuchat, Larry R.; Nail, B. V.

doi:10.4315/0362-028x-48.4.312

Cited by 14 publications

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“…A general conclusion emerged that antibiotic-supplemented media perform better than acidified media for determining populations in most types of foods. Nevertheless, it also has been shown repeatedly that for yeasts in certain low pH foods such as wines and fruit juices, acidified media recover numbers equal to those recovered on antibiotic-supplemented media (Beuchat and Nail 1985;Anderson and Moberg 1986;Deak et al 1986;Deak 1992). The results from the present study support these observations.…”

Section: Discussionsupporting

confidence: 85%

“…The recognition of sublethally-impaired cells is essential for the accurate assessment of the quality of foods. Most observations on injury and recovery of yeasts have been made on cells subjected to heat stress (Graumlich 1981 ;Stecchini and Beuchat 1985;Golden and Beuchat 1990); less information is available about freeze-injured yeasts (Beuchat and Nail 1985 ;.…”

Section: Introductionmentioning

confidence: 99%

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Comparison of conductimetric and traditional plating techniques for detecting yeasts in fruit juices

Deák

Beuchat

1993

Journal of Applied Bacteriology

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Frozen fruit juice concentrates containing an average microbial population of loglo 1-54 cfu ml-were examined by traditional plating techniques and direct and indirect conductimetry. T h e initial populations in diluted (1 : 4) concentrates increased to an average of loglo 3.82 cfu mlK during incubation at 25°C for 24 h. Incubation before plating and subjecting to conductimetric tests also facilitated the resuscitation of cells that may have been freeze-injured. Yeasts were recovered in equal numbers on acidified ( p H 3.5) potato dextrose agar and dichloran rose bengal chloramphenicol agar ( p H 5.6). Yeasts and bacteria were recovered on orange serum agar. Detection times determined by indirect conductimetry correlated fairly well (r = -0.73) with populations (cfu mi-') detected on traditional plating media. Populations in diluted concentrates which were not incubated before examination were detected conductimetrically in an average of 48.9 h, whereas detection times for diluted concentrates incubated for 24 h at 25°C before testing were reduced to an average of 14.1 h. Examination by conventional (direct) conductimetry required an additional 10-20 h to reach changes in conductance of 5 $3 h-'. ' 'Permanent address

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Section: Discussionsupporting

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Comparison of conductimetric and traditional plating techniques for detecting yeasts in fruit juices

Deák

Beuchat

1993

Journal of Applied Bacteriology

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“…Low concentrations of potassium phosphate (0.25%) have been shown to improve the recovery of freeze-injured Salmonella (27). Phosphate buffer (0.1 M) with or without 0.1% Tween 80 has been used as a diluent for recovering yeasts and molds from frozen fruit or fruit purees (3,5). Phosphate buffer (0.1 M) has been used to aid in the recovery of Salmonella spp., E. coli O157:H7, and Listeria monocytogenes from frozen and nonfrozen strawberries (18).…”

Section: Discussionmentioning

confidence: 99%

Phosphate Buffer Increases Recovery of Escherichia coli O157:H7 from Frozen Apple Juice

Yamamoto

Harris

2001

Journal of Food Protection

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It is common practice to dilute food products in 0.1% peptone before microbiological analysis. However, this diluent may not be appropriate for detection of injured organisms present in acidic foods. Shelf-stable unclarified apple juice (pH 3.6) was inoculated with approximately 1 x 10(7) CFU/ml of Escherichia coli O157:H7 and held at 23 +/- 2 degrees C (control) or frozen to -20 +/- 2 degrees C for 24 h to induce injury before sampling. Unfrozen or frozen and thawed juice was diluted 1:1 or 1:10 in 0.1% (wt/vol) peptone (pH 6.1) or 0.1 M phosphate buffer (pH 7.2). Juice samples were plated onto tryptic soy agar with 0.1% (wt/vol) sodium pyruvate (TSAP) to measure survival or onto sorbitol MacConkey agar (SMA) to indicate injury. Counts on TSAP or SMA were the same for control samples held in peptone or phosphate buffer for up to 45 min. However, populations of E. coli in frozen and thawed samples declined rapidly upon dilution in 0.1% peptone. Within 20 min, E. coli underwent a >1-log10 CFU/ml reduction in viability as measured on TSAP and a >2-log10 CFU/ml reduction to below the limit of detection (1.6 or 2.3 log10 CFU/ml) on SMA. In contrast, populations of E. coli in frozen and thawed samples diluted in phosphate buffer did not decrease significantly on TSAP and decreased by <0.6 log CFU/ml on SMA during a 45-min holding period. The acidity of apple juice appears to interfere with the recovery of freeze-thaw-injured E. coli O157:H7 during sampling. Using 0.1 M phosphate buffer (pH 7.2) as a diluent results in superior recovery of these organisms on both selective and nonselective plating media.

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“…Although optimum recovery conditions vary among species, incubation at neutral pH and 20-25 °C generally is favorable for recovery of stressed organisms. Beuchat and Nail (1985) evaluated yeast and mold recovery from fresh and frozen fruit purees using both acidified and antibiotic media. Acidified PDA yielded highest recovery of yeasts from fresh or frozen apple puree, while oxytetracycline-glucose-yeast extract agar (OGY), rose bengal-chloramphenicol agar, and dichloran-rose bengal-chloramphenicol agar supported greater mold recovery from fresh purees.…”

Section: Viable Countsmentioning

confidence: 99%

Processed Apple Products

Downing¹

1989

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Evaluation of Media for Enumerating Yeasts and Molds in Fresh and Frozen Fruit Purees

Cited by 14 publications

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Comparison of conductimetric and traditional plating techniques for detecting yeasts in fruit juices

Comparison of conductimetric and traditional plating techniques for detecting yeasts in fruit juices

Phosphate Buffer Increases Recovery of Escherichia coli O157:H7 from Frozen Apple Juice

Processed Apple Products

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