Rubén O. Morawicki

Analysis of microbial diversity on deli slicers using polymerase chain reaction and denaturing gradient gel electrophoresis technologies

Cross‐contamination of pathogenic and spoilage bacteria from food‐contact surfaces to food products is a serious public health issue. Bacteria may survive and attach to food‐contact surfaces by residual food components and/or background bacteria which may subsequently transfer to other food products. Deli slicers, generally used for slicing ready‐to‐eat products, can serve as potential sources for considerable bacterial transfer. The objective of this study was to assess the extent and distribution of microbial diversity of deli slicers by identification of pathogenic and background bacteria. Slicer‐swab samples were collected from restaurants in rkansas and Texas in the United States. Ten surface areas for each slicer were swabbed using sterile sponges. Denaturing gradient gel electrophoresis (DGGE) was applied to investigate the fingerprint of samples, and each band was further identified by sequence analysis. Pseudomonads were identified as the dominant bacteria followed by Enterobacteriaceae family, and lactic acid bacteria such as Lactococcus lactis and Streptococcus thermophilus were also found. Bacterial distribution was similar for all surface areas, while the blade guard exhibited the greatest diversity. This study provides a profile of the microbial ecology of slicers using DGGE to develop more specific sanitation practices and to reduce cross‐contamination during slicing.

Enzymatic hydrolysis of poultry meal with endo- and exopeptidases

The objective of this research was to determine whether commercial proteases are capable of hydrolyzing denatured poultry by-product proteins that have gone through a rendering process. The material used for this research was low-ash poultry meal obtained from a local poultry processor. Samples of poultry meal were treated with the commercial proteases Alcalase, Flavourzyme, Protamex, and Liquipanol that were added individually or as a combination of 2 proteases, which were incorporated either simultaneously or sequentially. Temperature was controlled during the reaction to the optimal level for each enzyme, and pH was initially adjusted to the most favorable level for each enzyme and was maintained during the course of the reaction by addition of NaOH at established intervals. Consumption of NaOH was used to calculate the degree of hydrolysis. At the end of the hydrolysis, the molecular weight of selected hydrolysates was determined by size exclusion chromatography and by gel electrophoresis. In addition, amino acid analysis was performed on selected hydrolysates. Results show that the sequential treatment with Alcalase and Flavourzyme served best for the preparation of poultry meal hydrolysates with a maximum degree of hydrolysis of 11.1% and the highest hydrolyzable material recovered at 58%, which is attributed to the combined nature of the endo- and exocatalytic action of Alcalase and Flavourzyme, respectively. Hydrolysate with Flavourzyme or the combination of Flavourzyme and Alcalase were both good methods to produce significant amounts of free amino acids. This research shows the feasibility of hydrolyzing poultry by-products that went through a rendering process using different brands of commercial proteases. Findings from this research are important in the preparation of palatants, in which relatively inexpensive hydrolyzed poultry meal could be used to improve the flavor of companion animal food products.

Hydrolysis of Whey Protein Isolate Using Subcritical Water

Hydrolyzed whey protein isolate (WPI) is used in the food industry for protein enrichment and modification of functional properties. The purpose of the study was to determine the feasibility of subcritical water hydrolysis (SWH) on WPI and to determine the temperature and reaction time effects on the degree of hydrolysis (DH) and the production of peptides and free amino acids (AAs). Effects of temperature (150 to 320 °C) and time (0 to 20 min) were initially studied with a central composite rotatable design followed by a completely randomized factorial design with temperature (250 and 300 °C) and time (0 to 50 min) as factors. SWH was conducted in an electrically heated, 100-mL batch, high pressure vessel. The DH was determined by a spectrophotometric method after derivatization. The peptide molecular weights (MWs) were analyzed by gel electrophoresis and mass spectrometry, and AAs were quantified by high-performance liquid chromotography. An interaction of temperature and time significantly affected the DH and AA concentration. As the DH increased, the accumulation of lower MW peptides also increased following SWH (and above 10% DH, the majority of peptides were <1000 Da). Hydrolysis at 300 °C for 40 min generated the highest total AA concentration, especially of lysine (8.894 mg/g WPI). Therefore, WPI was successfully hydrolyzed by subcritical water, and with adjustment of treatment parameters there is reasonable control of the end-products.

Tolerance of S. cerevisiae and Z. mobilis to inhibitors produced during dilute acid hydrolysis of soybean meal.

The objective of this research was to determine the minimum inhibitory concentration of 5-hydroxymethyl furfural, furfural, and acetic acid on Saccharomyces cerevisiae (NRRL Y-2233) and Zymomonas mobilis subspecies mobilis (NRRL B-4286) in both detoxified hydrolyzed soybean meal and synthetic YM broth spiked with the three compounds. Soybean meal was hydrolyzed with dilute sulfuric acid (0.0, 0.5, 1.25, and 2.0% wt v−1) at three temperatures (105, 120, and 135°C) and three durations (15, 30, and 45 min) followed by detoxification with activated carbon. Of all the combinations, only the treatments obtained at 135°C, 2.0% H2SO4, and 45 min and the one at 135°C, 1.25% H2SO4, and 45 min showed inhibition in the growth of the tested microorganisms. Spiked YM broths showed inhibition for the highest levels of inhibitors, either applied individually or in combination.

Antimicrobial Activities of Phenolic Extracts Derived from Seed Coats of Selected Soybean Varieties: Antimicrobial of soy seed coat extracts…

Soybean hulls or seed coats consist of complex carbohydrates, proteins, lipids, and polyphenols such as anthocyanidins, proanthocyanidins, and isoflavones. The polyphenolics in the seed coats give them various colors such as black, brown, green, yellow, or even a mottled appearance. In this study, the antimicrobial effects of phenolic extracts from the seed coats of different colored soybeans (yellow, dark brown, brown, and black) were evaluated against foodborne pathogens such as Salmonella Typhimurium, Escherichia coli O157:H7, and Campylobacter jejuni in broth-cultures as well as on chicken skin. The highest total phenolic content was observed for the phenolic extract from soybean variety (R07-1927) with black colored seed coat (74.1 ± 2.1 mg chlorogenic acid equivalent [CAE]/g extract) and was significantly different (P <0.0001) from the extract of the conventional soybean variety (R08-4004) with yellow colored seed coat (7.4 ± 1.2 mg CAE/g extract). The extract from black colored soybean produced reductions of 2.10 ± 0.08 to 2.20 ± 0.08-log CFU/mL for both E. coli O157:H7 and C. jejuni after 3 d when incubated in broth-culture having 4-log CFU/mL of bacteria, whereas a 6 d incubation was found to reduce S. Typhimurium and E. coli O157:H7 at 2.03 ± 0.05 and 3.3 ± 0.08-log CFU/mL, respectively. The extract also reduced S. Typhimurium and E. coli O157:H7 attached to chicken skin by 1.39 ± 0.03 and 1.24 ± 0.06-log CFU/g, respectively, upon incubation for 6 d. Soybean seed coat extracts may have a potency as antimicrobial agents to reduce foodborne bacteria contaminating poultry products.

Sampling and Sample Preparation

Food quality is monitored at various processing stages, but 100% inspection is rarely possible, or even desirable. To ensure a representative sample of the population is obtained for analysis, sampling and sample reduction methods must be developed and implemented. Sampling is a vital process, since it is often the most variable step in the entire analytical procedure. The selection of the sampling procedure is determined by the purpose of the inspection, the nature of the population and product, and the test method. This chapter covers various aspects of sampling to be considered: homogenous vs. heterogeneous samples; discrete vs. continuous populations; sampling for attributes vs. variables; consumer risk vs. vendor risk of sampling; manual vs. continuous sampling; probability vs. nonprobability sampling; numerous choices of sampling plans; and precision analysis vs. power analysis to estimate sample size. Challenges continue after the sample is collected, including proper sample storage and identification, often followed by sample size reduction to an amount suitable for sample preparation. That sample preparation often involves grinding to a particle size appropriate for analysis then storage prior to analysis, both of which must be done in ways to prevent sample degradation. The principles described in this chapter are intended to provide a basis for understanding, developing, and evaluating sampling plans and sample handling procedures for specific food analysis applications.

Impact of milling and water-to-rice ratio on cooked rice and wastewater properties

Due to the environmental concerns and expense associated with the disposal of wastewater after industrial cooking of rice, the purpose of this study was to evaluate the extent of leaching, water uptake and volumetric expansion of rice during cooking at various milling durations and water-to-rice ratios. Two cultivars of Arkansas rice, a long grain (Francis) and a medium grain (Jupiter), were milled for 10, 20, and 30 s with a laboratory mill. Samples were cooked in aluminum foil covered beakers at water-to-rice ratios of 10:1, 15:1, and 20:1. After 20 min, rice was weighed for water uptake and measured for volumetric expansion using hexane displacement. The excess cooking water was evaluated for total solids, amylose, and protein to determine the extent of leaching. Water uptake and volumetric expansion significantly increased with milling duration in both cultivars. Leached solids increased as the water-to-rice ratio increased in Francis and increased with milling duration in Jupiter; however, the amylose content of leached solids was unaffected by the water-to-rice ratio in both cultivars. Thus, shorter milling durations may limit the extent of leaching during cooking, as observed with Jupiter, while a lower water-to-rice ratio may reduce wastewater contamination for cultivars similar to Francis.

Effects of Fermentation by Yeast and Amylolytic Lactic Acid Bacteria on Grain Sorghum Protein Content and Digestibility

Despite many advantages to its cultivation, grain sorghum is an underutilized crop because of low nutrient availability, particularly protein digestibility, due to antinutritional compounds in the grain and by moist-heat cooking. Some of these concerns can be mitigated by how the grain is processed. Fermentation is one processing method that can improve digestibility and at the same time concentrate protein in a substrate. In this experiment, grain sorghum was subjected to different treatments and fermented with baker’s yeast (Saccharomyces cerevisiae) and an amylolytic species, Lipomyces kononenkoae, to improve and increase protein content. The effects of pasteurization or sterilization of the substrate, nitrogen supplementation, amyloglucosidase addition, and coculture with Lactobacillus amylovorus were examined. After fermentation, baker’s yeast samples treated with enzyme increased in crude protein, from 9% in unfermented grain to approximately 27% after treatment. Nitrogen supplementation accelerated protein enrichment and was a significant factor at 24 hours of fermentation. Both types of yeast increased pepsin digestibility of sorghum protein compared to thermally processed control samples. The ratio of phytate to protein was reduced by both yeast species. L. kononenkoae reduced phytates in the substrate but did not enrich protein content. The lactic coculture had no significant effect on measured responses.

The Elimination of Listeria Monocytogenes Attached to Stainless Steel or Aluminum Using Multiple Hurdles

UNLABELLED Ready-to-eat luncheon meats sliced in retail delis have been found to pose the greatest risk of foodborne illness from Listeria monocytogenes among all ready-to-eat foods. Slicers used in delis have many removable parts that are connected with seals and gaskets, with spaces, cracks and crevices that are difficult to clean adequately and may provide a niche for L. monocytogenes survival. Standard cleaning and sanitizing practices used by deli employees may not eliminate Listeria in these niches. Moist heat is known to be more effective against L. monocytogenes than dry heat at the same temperature and time. The study reported here investigated the effects of moist heat combined with quaternary ammonium compounds (5 or 10 ppm), chlorine (10 or 25 ppm) or peracetic acid (10 or 25 ppm) on inactivating L. monocytogenes attached to stainless steel or aluminum coupons cut from commercial deli meat slicer components. All sanitizers when used alone resulted in a 2- to 3-log reduction of L. monocytogenes on stainless steel or aluminum surfaces, while moist heat alone resulted in a 3- to 4-log reduction. When combined with heat the quaternary ammonium was used at 5 ppm, peracetic acid at 10 ppm and chlorine at 10 ppm. When the 2 lethal treatments were combined there was a 5- to7-log reduction as compared to initial inoculation. PRACTICAL APPLICATION The results of this study will provide a better understanding and potential methods for the sanitization of industrial deli meat slicers. In turn, the knowledge gained from this study can reduce the risk of contamination and outbreaks of L. monocytogenes and other food-borne pathogens for consumers.

The effect of adaptation of Lactobacillus amylovorus to increasing concentrations of sweet potato starch on the production of lactic acid for its potential use in the treatment of cannery waste

Abstract Lactobacillus amylovorus, an amylolytic species, was cultured in increasing concentrations of sweet potato starch to test the effect of this progressive acclimation on lactic acid production. This research is part of a project on the use of the waste stream from a sweet potato cannery to produce lactic acid. The media used for this acclimation was a modified version of the de Man, Rogosa and Sharpe medium, in which glucose was partially or totally substituted with sweet potato starch. The process was done in five steps, starting with 100% glucose in the first step and ending with 100% sweet potato starch in the last one. At each step, the effectiveness of the acclimation was tested by running fermentations with and without pH control for 62 h. The effect of the overall adaptation process was tested by comparing the growth and activity of the acclimated vs non-acclimated bacteria using sweet potato starch as the only source of carbohydrates. Growth and activity assessments indicated that L. amylovorus was able to ferment sweet potato starch into lactic acid. In most cases, pH control resulted in better substrate utilisation and larger amounts of lactic acid. In the comparison study, however, the adaptation process had a major influence on lactic acid production than the effect of pH. For 20 g L–1 sweet potato starch media, adapted L. amylovorus under no pH control yielded 11.20 g L–1 versus the non-adapted bacteria, which yielded 7.10 g L–1. Under controlled pH conditions, 14.80 and 4.20 g L–1 lactic acid were produced by adapted and non-adapted bacteria respectively.