Bee K. May

The importance of considering exchange surface area reduction to exhibit a constant drying flux period in foodstuffs

Abstract In this study, experimental data on the shrinkage of potato, carrot, apple and avocado using high-speed laser scan micrometers are presented. These devices allow the exchange surface area to be evaluated at any time. Results of convective drying trials show consistently that a constant drying flux period does exist provided the actual exchange surface area is considered. Most numerical models tend to neglect the shrinkage factor for ease of solving the model equations. We have shown in this study that such an approach is only valid for products that have a very small shrinkage factor. In the case of foodstuffs with high initial moisture content and therefore having a high tendency to shrink, the model must incorporate the shrinkage factor for it to reflect the reality. Using these experimental values, a critical moisture content, very different from that generally proposed in the literature, was exhibited.

A NUMERICAL DRYING MODEL THAT ACCOUNTS FOR THE COUPLING BETWEEN TRANSFERS AND SOLID MECHANICS. CASE OF HIGHLY DEFORMABLE PRODUCTS

Derived from a previous version of TransPore, the numerical model presented in this work has been developed in order to describe the drying of porous media that undergo large deformations due to shrinkage. For such products, the change of geometrical shape has to be taken into account to solve the balance equations. The initial product shape is described using triangular elements. From this classical FE mesh, Control Volumes are built and used to solve heat and mass transfer equations, while the initial FE mesh is used to solve the mechanical problem. Due to large shrinkage values, non-linear problems arise from the large strain field generated during the process. In order to overcome this difficulty, the constitutive law is written on a local intermediate configuration in which rotation is chosen to oppose the rotation appearing in the polar decomposition of the deformation gradient tensor. One typical example is presented for potato. This product has its most part of shrinkage within the domain of free water. Consistently, the sample shape varies significantly although free water remains available at the exchange surface. Paradoxical results can be obtained when simulating low convective drying of this product: a decreasing drying rate flux is exhibited during the first drying period. This paradox, which has also been observed during experiments, is obviously due to the reduction of the exchange surface.

The behaviour of whey protein isolate in protecting Lactobacillus plantarum

There is increasing evidence that whey protein isolates (WPI), can be utilised to encapsulate and protect bioactive substances, including lactic acid bacteria, due to their physicochemical properties. However, little is known about what happens in the immediate vicinity of the cells. This study examined the protective behaviour of WPI for two strains of Lactobacillus plantarum, A17 and B21, during spray drying. B21 was found to be more hydrophobic than A17 and required 50% of the amount of WPI to provide comparably high survival (∼ 90%). We hypothesise that WPI protects the hydrophobic bacteria by initial attachment to the unfolded whey protein due to hydrophobic interactions followed by adhesion to the proteins, resulting in cells being embedded within the walls of the capsules. The encapsulated strains had a moisture content of approximately 5.5% and during storage trials at 20 °C retained viability for at least eight weeks.

Complete Genome Sequence of Lactobacillus plantarum Strain B21, a Bacteriocin-Producing Strain Isolated from Vietnamese Fermented Sausage Nem Chua

ABSTRACT Lactobacillus plantarum strain B21 was isolated from Vietnamese sausage (nem chua) and demonstrated broad antimicrobial activity due to the production of bacteriocins. Here, we report the complete genome sequence of this strain (3,284,260 bp).

QUANTITATIVE ANALYSIS OF DRYING BEHAVIOUR OF FRUITS AND VEGETABLES

ABSTRACT In this study, the drying characteristics of seven vegetables (garlic, potato, bean. ginger, leek, onion, and carrot) and five fruits (avocado, banana, sultana, kiwi fruit and apple) were studied under idealised ‘constant’ controlled drying conditions using an automatic thermogravimetric analyser. Drying-rate curves were constructed and quantified in a systematic way using the least-squares method. This allowed the drying behaviour of each product to be expressed in terms of three variables; gradient of the “constant rate” stage, gradient of the falling rate stage and critical moisture content (CMC) The drying curves of fruits and vegetables were found to vary greatly indicating the nature of foodstuffs to have a strong effect on the drying kinetics. The gradient of the constant rate period was not truly constant but had an average gradient of 3.1 × 10−4 per second with bean having the lowest gradient (1.9 × 10 −4/) and garlic having the highest gradient (5.3 × 10−4/s). This was expected as bean ...

The Efficacy of Chlorinated Water Treatments in Minimizing Yeast and Mold Growth in Fresh and Semi-dried Tomatoes

Abstract A key problem with dried tomatoes for the industries is that the products tend to have limited shelf-life due to yeast and mold growth. This study was undertaken to evaluate the efficacy of chlorine treatments on minimizing yeast and mold populations on fresh and semi-dried tomatoes. Tomatoes were inoculated with molds (4.2 log CFU/g) from contaminated pack of semi-dried tomatoes. These inoculated tomatoes were then treated by washing with water (control) and concentrations of 50, 100, and 200 ppm of chlorinated water for specific length of time (1, 5, and 10 min), and finally analyzed for yeast and mold populations. In this study, the results showed that the maximum log reduction of yeast and mold cells on tomato surface was found to be chlorinated water with a concentration of 200 ppm. At this concentration, washing for 5 and 10 min resulted in 1.7 log reduction and 3.1 log reduction in yeast and mold growth respectively. This was significant (P<0.01) as compared with washing with tap water (control). Drying at 60°C further reduce the microbial load of these pre-treated tomatoes. Results showed that there were reductions in three of the twelve runs while seven of the runs demonstrated an increase in microbial load. This finding is important as it demonstrated that when using a typical drying temperature of 60°C, if the initial microbial load is high, there is a risk that the dehydrator can act as an incubator for more microbial growth. This finding also demonstrated the importance of pretreatment to reduce the initial microbial load before drying commences.

A STUDY OF TEMPERATURE AND SAMPLE DIMENSION IN THE DRYING OF POTATOES

Abstract It is common knowledge that sample size and drying temperature are two of the most important factors affecting the drying rate and quality of food. However, what is less commonly known are how these two factors interact relative to each other and their effects on the drying behaviour of potato. These effects were evaluated under controlled drying conditions using a thermogravimetric analyser. The least-squares method was used to fit a model to the experimental data and the response variables (slope of the first drying stage, transition moisture content and slope of the second drying stage) were determined systematically. Central composite design was applied for response surface modelling of the factors and regression methodology was used to analyse the results. The results showed that both temperature and sample dimension have significant (P=0.01) effect on drying behaviour of potato. Sample dimension significantly affected the transition moisture content, whilst both temperature and sample dimension significantly affected the slopes of the first and second stage of drying.

pH-induced structural changes of apo-lactoferrin and implications for its function: a molecular dynamics simulation study

ABSTRACT The minor protein in milk, lactoferrin (Lf), is known for a variety of biological functions, and has been investigated as a protective encapsulant for probiotic bacteria in health-promoting food products. Lf is likely to be exposed to extreme pH conditions which are known to have disruptive influences on its functionality. The molecular mechanisms underlying these pH-dependent changes are not well-understood. To explore the potential of Lf as an encapsulant, molecular dynamics (MD) simulations were applied to study its conformational changes under extreme acidic (pH 1.0) or basic (pH 14.0) conditions, relative to neutral pH. Simulations indicate that the structure of apo-Lf is relatively stable at neutral pH, while acidic and basic pH result in substantially greater flexibility, partly induced by the loss of contacts between the N- and C-terminal lobes, causing them to undergo extensive relative bending and twisting motions. Basic pH causes greater structural disruption compared to acidic exposure. The latter has greater influence on the N-terminus, with increased fluctuations and disruptions of inter-residue contacts compared to those at neutral pH; while basic pH was found to more prominently disrupt contacts at the C-terminus. These results help elucidate possible functional consequences on Lf of exposure to extreme pH conditions.

Draft genome sequence of Lactobacillus plantarum strain A6, a strong acid producer isolated from a Vietnamese fermented sausage (nem chua)

ABSTRACT Lactobacillus plantarum strain A6, a strong acid producer, was isolated from a Vietnamese fermented sausage (nem chua). Here, we report the genome sequence of this strain (3,368,579 bp).