Amalia G.M. Scannell

Development of bioactive food packaging materials using immobilised bacteriocins lacticin 3147 and nisaplin.

Immobilisation of the bacteriocins nisin and lacticin 3147 to packaging materials was investigated. Stability of both cellulose-based bioactive inserts and anti-microbial polyethylene/polyamide pouches was examined over time. Anti-microbial activity against the indicator strain Lactococcus lactis subsp. lactis HP, in addition to Listeria innocua DPC 1770 and Staphylococcus aureus MMPR3 was observed for all bacteriocin-adsorbed materials. Activity retention of the inserts showed an initial decrease in the first week of storage but remained stable for the remaining 3 months of the trial. However, adsorption of lacticin 3147 to plastic film was unsuccessful, nisin bound well and the resulting film maintained its activity for 3-month period, both at room temperature and under refrigeration. When applied to food systems, the anti-microbial packaging reduced the population of lactic acid bacteria in sliced cheese and ham stored in modified atmosphere packaging (MAP) at refrigeration temperatures, thus extending the shelf life. Nisin-adsorbed bioactive inserts reduced levels of Listeria innocua by > or = 2 log units in both products, and Staphylococcus aureus by approximately 1.5 log units in cheese, and approximately 2.8 log units in ham. Similar reductions were observed in cheese vacuum-packaged in nisin-adsorbed pouches.

Near-infrared hyperspectral imaging and partial least squares regression for rapid and reagentless determination of Enterobacteriaceae on chicken fillets.

Bacterial pathogens are the main culprits for outbreaks of food-borne illnesses. This study aimed to use the hyperspectral imaging technique as a non-destructive tool for quantitative and direct determination of Enterobacteriaceae loads on chicken fillets. Partial least squares regression (PLSR) models were established and the best model using full wavelengths was obtained in the spectral range 930-1450 nm with coefficients of determination R(2)≥ 0.82 and root mean squared errors (RMSEs) ≤ 0.47 log(10)CFUg(-1). In further development of simplified models, second derivative spectra and weighted PLS regression coefficients (BW) were utilised to select important wavelengths. However, the three wavelengths (930, 1121 and 1345 nm) selected from BW were competent and more preferred for predicting Enterobacteriaceae loads with R(2) of 0.89, 0.86 and 0.87 and RMSEs of 0.33, 0.40 and 0.45 log(10)CFUg(-1) for calibration, cross-validation and prediction, respectively. Besides, the constructed prediction map provided the distribution of Enterobacteriaceae bacteria on chicken fillets, which cannot be achieved by conventional methods. It was demonstrated that hyperspectral imaging is a potential tool for determining food sanitation and detecting bacterial pathogens on food matrix without using complicated laboratory regimes.

Evaluation of the effects of fat replacers on the quality of wheat bread

The performance of different fat replacers at various levels (Inulin powder, Inulin gel and Simplesse) in wheat bread and dough compared to a control containing block fat was examined. Empirical and fundamental rheological tests were carried out on the doughs. Volume yield, crumb texture, crust colour and crumb image characteristics were measured for the baked loaves. The addition of inulin gel was found to increase water absorption. Dough complex modulus for doughs containing fat was significantly lower (P<0.01) than the doughs containing the replacers. The addition of simplesse and inulin increased the complex modulus (P<0.01). Loaves containing the control fat and inulin gel had similar volume yields, significantly higher (P<0.01) than loaves containing simplesse or inulin powder. Inulin powder and simplesse had adverse effects on crumb hardness, producing slices significantly harder (P<0.01) than slices with the control fat or inulin gel. Overall it was found that breads containing the inulin gel were similar in quality characteristics to the control breads containing fat.

Determination of the influence of organic acids and nisin on shelf-life and microbiological safety aspects of fresh pork sausage

The effect of replacing sulphur dioxide with organic acids and nisin to reduce the microbialcounts in fresh pork sausage was examined. The potential of sodium citrate or sodium lactate,used singly or in combination with nisin, was also assessed in sausage inoculated with Staphylococcus aureus MMPR 3 and Salmonella kentucky AT 1. The results indicatethat a combination of sodium lactate and nisin was particularly effective in reducing total bacterialcounts in this food product. It also appears that this combination provides an increased protectionagainst common pathogenic contaminants of fresh pork sausage, i.e. Staph. aureus and Salmonella species.

Modelling of yeast inactivation in sonicated tomato juice

Power ultrasound is recognised as a potential non thermal technique to inactivate microorganisms pertinent to fruit juices. In this study, the effect of sonication on the resistance of yeast (Pichia fermentans) in tomato juice was investigated. Tomato juice samples were sonicated at amplitude levels ranging from 24.4 to 61.0mum at a constant frequency of 20kHz for different treatment times (2 to 10min) and pulse durations of 5s on and 5s off. Significant reductions (p<0.05) were observed at higher amplitudes and processing times. Yeast inactivation was found to follow the Weibull model with a high regression coefficient (R(2)>0.98) and low RMSE (<0.51). The desired 5 log reductions (D(5) value) and shape factors were found to correlate exponentially with amplitude level. Results presented in this study show that sonication alone is an effective process to achieve the desired level of yeast inactivation in tomato juice.

Use of response surface methodology to produce functional short dough biscuits

Abstract The objective of this study was to develop a biscuit containing reduced fat and sugar levels as well as exhibiting ‘functional’ properties. A basic short dough formulation was used as a control. An experimental design was utilised to optimise the levels of Novelose 330 (resistant starch), Raftilose (sugar replacer/fructooligosaccharide), sodium caseinate (dairy protein) and Simplesse (protein-based fat replacer) in the production of a functional low fat and sugar biscuit. Parameters measured were dough characteristics, biscuit dimensions, colour, and texture. Sodium caseinate was found to be an important determinant for dough hardness. A positive correlation was revealed between biscuit thickness and texture (P L ∗ (surface colour) ranged from 41.1 to 52.2, depending upon the quantities of sugar and protein powder present. Optimal ingredient levels were found to be 14% Novelose (% flour), 14.51% sodium caseinate (% flour), 25% Raftilose (% sugar) and 25.02% Simplesse (% fat). Such levels produce a biscuit of extremely high standard.

An effective lacticin biopreservative in fresh pork sausage.

Lacticin 3147 is a novel heat-stable bacteriocin, produced by Lactococcus lactis DPC 3147, that exhibits a broad-range inhibition spectrum similar to nisin. In this study, the effect of lacticin 3147 and nisin on the shelf life of fresh pork sausage and their ability to control pathogens (Clostridium perfringens DSM 756, Salmonella Kentucky AT1) and nonpathogenic Listeria innocua DPC 1770 was investigated. The following preservative regimens were evaluated, both in broth and sausage systems: (i) 450 ppm of sodium metabisulphite; (ii) 500 IU g(-1) or ml(-1) of nisin, (iii) 2500 arbitary units (AU) g(-1) or ml(-1) of lacticin 3147; (iv) 2% sodium lactate and 500 IU of nisin; (v) 2% sodium citrate and 500 IU g(-1) or ml(-1) of nisin; (vi) 2% sodium lactate and 2500 AU g(-1) or ml(-1) of lacticin 3147, (vii) 2% sodium citrate and 2500 AU g(-1) or ml(-1) of lacticin 3147, (viii) 2% sodium lactate, and (ix) 2% sodium citrate. There was no significant difference in the activity of nisin and lacticin 3147 against any of the target strains used, both bacteriocins performing significantly better than sodium metabisulfite against gram-positive strains in broth systems. Trends indicate that the combination of organic acids with either bacteriocin enhanced its activity against Salmonella Kentucky and L. innocua and was particularly effective in the inhibition of C. perfringens in fresh pork sausage. In addition, lacticin 3147 combined with either sodium citrate or sodium lactate maintained significantly lower (P < 0.05) total aerobic plate counts for the duration of the trials and may function as an alternative to sodium metabisulfite in the preservation of fresh pork sausage.

Evaluation of sugar replacers in short dough biscuit production

Sugar inhibits gluten development during dough mixing by competing with the flour for the recipe water, resulting in less tough and more crumbly biscuits. Commercially available Raftilose, which acts as an oligofructose and a sugar replacer was used in the recipes where the sugar was reduced by 20-30%. It was found that the sugar replacer did not exert the same hardening effect on the dough as the granulated sugar, therefore values for dough hardness were found to be lower than those obtained for the standard biscuit. Peak force values of the reduced sugar biscuits were found to be significantly lower than the control biscuit (P < 0.05), indicating a lower snapping characteristic, and therefore softer eating characteristics. Only those biscuits with the highest level of sugar replacement showed different surface colour attributes. At the lower and medium levels of sugar replacement, oligofructose can be used successfully to reduce sugar in short dough biscuits.

PEF based hurdle strategy to control Pichia fermentans, Listeria innocua and Escherichia coli k12 in orange juice.

The combination of pulsed electric fields (PEF) and bacteriocins in a hurdle approach has been reported to enhance microbial inactivation. This study investigates the preservation of orange juice using PEF in combination with nisin (2.5 ppm), natamycin (10 ppm), benzoic acid (BA; 100 ppm), or lactic acid, (LA; 500 ppm). Pichia fermentans, a spoilage yeast frequently isolated from orange juice, Escherichia coli k12 or Listeria innocua were inoculated into sterile orange juice (OJ) with, and without, added preservatives. The antimicrobial activity over time was evaluated relative to an untreated control. The effect of PEF treatment (40 kV/cm, 100 micros; max temperature 56 degrees C) was assessed on its own, and in combination with each antimicrobial. The acidic environment of OJ inactivated E. coli k12 (1.5log reduction) and L. innocua (0.7log reduction) slightly but had no effect on P. fermentans. PEF caused a significant decrease (P<0.05) in the viability of P. fermentans, L. innocua and E. coli k12 achieving reductions of 4.8, 3.7 and 6.3log respectively. Nisin combined with PEF inactivated L. innocua and E. coli k12 in a synergistic manner resulting in a total reduction to 5.6 and 7.9log respectively. A similar synergy was shown between LA and PEF in the inactivation of L. innocua and P. fermentans (6.1 and 7.8log reduction), but not E. coli k12. The BA-PEF combination caused an additive inactivation of P. fermentans, whereas the natamycin-PEF combination against P. fermentans was not significantly different to the effect caused by PEF alone. This study shows that combining PEF with the chosen preservatives, at levels lower than those in current use, can provide greater than 5log reductions of E. coli k12, L. innocua and P. fermentans in OJ. These PEF-bio-preservative combination hurdles could provide the beverage industry with effective non-thermal alternatives to prevent microbial spoilage, and improve the safety of fruit juice.

Detection and Identification of Bacteria in an Isolated System with Near-Infrared Spectroscopy and Multivariate Analysis

Near-infrared (NIR) transflectance spectra of Listeria innocua FH, Lactococcus lactis, Pseudomonas fluorescens, Pseudomonas mendocina, and Pseudomonas putida suspensions were collected and investigated for their potential use in the identification and classification of bacteria. Unmodified spectral data were transformed (first and second derivative) using the Savitzsky-Golay algorithm. Principal component analysis (PCA), partial least-squares discriminant analysis (PLS2-DA), and soft independent modeling of class analogy (SIMCA) were used in the analysis. Using either full cross-validation or separate calibration and prediction data sets, PLS2 regression classified the five bacterial suspensions with 100% accuracy at species level. At Pseudomonas genus level, PLS2 regression classified the three Pseudomonas species with 100% accuracy. In the case of SIMCA, prediction of an unknown sample set produced correct classification rates of 100% except for L. innocua FH (77%). At genus level, SIMCA produced correct classification rates of 96.7, 100, and 100% for P. fluorescens, P. mendocina, and P. putida, respectively. This successful investigation suggests that NIR spectroscopy can become a useful, rapid, and noninvasive tool for bacterial identification.