FORCE-DEFORMATION CONDITIONS ASSOCIATED WITH THE EVALUATION OF BRITTLENESS AND CRISPNESS IN SELECTED FOODS1

The brittleness and crispness of low moisture foods and the crispness of selected high moisture foods were evaluated both instrumentally by Instron fracture tests and using a sensory panel. Brittleness was evaluated sensorially during the “first bite” whereas crispness was identified at a later stage of mastication. The maximum force at fracture of low moisture foods correlated inversely with panelists’ evaluations of brittleness either in the mouth or using the fingers. Panelists' evaluations of crispness in the mouth correlated reasonably well with the initial linear portion of the Instron force-deformation curves when the sample were supported near their ends and also in their middle regions. The shapes of the force-deformation curves for high moisture foods were very much influenced by the way in which samples were supported in fracture tests, the method of fracture and the Instron cross-head speed.     

A STUDY OF FORCE-COMPRESSION CONDITIONS ASSOCIATED WITH HARDNESS EVALUATION IN SEVERAL FOODS

Abstract. The hardness of fourteen foods has been evaluated by panel tests and by compression tests with a table model Instron. Oral evaluation of hardness was correlated with instrumental force -% compression data obtained for compressions extending up to 80% and with crosshead speeds up to 20 cm min⁻¹. With soft foods, agreement between panelists' and instrumental data commences at lower % compressions and lower applied forces than with hard foods. As the Instron crosshead speed increases so does the force required to achieve a desired % compression. With very hard foods exhibiting a short relaxation time, e. g. toffee, stress relaxation may influence the registered force. Crosshead speeds exceeding 20 cm min^-1** cannot be utilised in conjunction with the standard Instron recorder because its response time is too long. It should be replaced by a fast response recorder such as a UV recorder. The procedure whereby panelists evaluate hardness during the first downstroke of mastication appears to change from compression to biting as hardness increases. A limited number of tests with Cheddar cheese and table jelly suggest that hardness evaluation by squeezing samples between the thumb and index finger involves lower % compression and lower forces than the oral evaluation of hardness with the same products.     

CONTINUOUS FERMENTATION OF GLUCOSE SOLUTIONS

Use of a continuous-flow plug fermentor to ferment glucose solutions was found to be possible only with unrefined commercial glucose and not with pure glucose. Even when the former was used problems were encountered due to a gradual increase in back pressure across the yeast bed. With the commencement of glucose metabolism in the yeast bed, ‘shock’ excretion of potassium and magnesium ions as well as of low molecular weight nitrogenous material was observed. The product from the fermentor contained an abnormally high level of α-diketones viz., 1–3 mg/litre.     

IDENTIFICATION OF STIMULI CONTROLLING THE SENSORY EVALUATION OF VISCOSITY II. Oral Methods

The stimulus associated with oral evaluation of the viscosity of liquid and viscous foods appears to embrace a range of shear rates extending from 10^-1 to 1000 s^-1. The value associated with a particular food depends on its flow characteristics. For liquid foods the stimulus appears to be the shear rate developed at an approximately constant shear stress (～ 100 dyn cm^-2), whereas for viscous foods it appears to be the shear stress developed at an approximately constant shear rate (～ 10 s^-1). Additional factors may be involved when evaluating highly viscous non-Newtonian foods or foods with an oil continuous medium. These are ‘plug flow’ or the spreading coefficient, respectively.     

IDENTIFICATION OF STIMULI CONTROLLING THE SENSORY EVALUATION OF VISCOSITY I. Non-Oral Methods

Flow properties of several liquid and semi-solid foods were characterized objectively with a coaxial cylinder viscometer. At the same time, a sensory evaluation panel compared the viscosities of these samples by tilting the containers and also by stirring the contents with a spoon. Correlation of the instrumental and sensory evaluation data established the shear stress-shear rate conditions prevailing during sensory evaluation of viscosity. The stimulus responsible for viscosity evaluation by tilting the container is the shear rate (0.1–40 sec^-1) developed at a shear stress (60–600 dyne cm^-2) related to the flow properties of the sample, whereas in stirring tests the stimulus is the shear stress (10²–10⁴ dyne cm^-2) developed at a particular rate of shear (90–100 sec^-1). In the latter type of test, the shear rate varies to some degree with the flow characteristics of the sample. Since different stimuli are involved in viscosity assessment by tilting the container or by stirring, it is possible for a series of samples to be given different ranking orders by the two methods of evaluation.     

SURFACE HEAT TRANSFER COEFFICIENTS ASSOCIATED WITH HEATING of FOOD PARTICLES IN CMC SOLUTIONS

The fluid-to-particle heat transfer coefficients (h_fp) associated with the heating of cylindrical specimens of potato and carrot were evaluated in carboxy-methylcellulose (CMC) solutions (0–1%) at 50–80C. Average h_fp values ranged from 80 to 450 W/m²C for potatoes and 100 to 550 W/m²C for carrots. Temperature and concentration of CMC influenced its power law parameters and hence. h_fp values while fluid velocity (0.2 to 0.7 × 10^?3 m/s), sample size (0.016–0.023 m diameter, 0.02–0.04 m length) and flow direction (upward and downward) had marginal effects. Natural convection dominated the flow regime, giving good correlations between Nusselt and Rayleigh numbers.     

PERFORMANCE AND MICROBIOLOGICAL GROWTH IN GROUND MEAT ASSOCIATED WITH THE USE OF THAWING TRAYS

The study goal was to determine whether trays marketed to hasten thawing of food would perform safely. Three brands of trays (Miracle Thaw, Super Defrost, and Defrost Master 2000) and aluminum skillets were purchased for experiments. Four frozen burgers with thermocouples inserted were placed onto a thawing device to thaw to 2.78C internal temperature. Experiments were replicated. Time and temperature (ambient, surface, internal) were recorded. Prethawing and thawed samples were analyzed for aerobic plate counts. Regression models were developed to identify sources of variation in time to thaw burgers, total bacterial count, and change in count pre/post thawing. All trays and aluminum skillets thawed burgers equally well (P>.05). Meat thawed within two hours (mean 83.6 min, maximum 119 min). Aerobic plate counts did not indicate spoilage of meat (mean 2372 cfu/g, maximum 17600 cfu/g). Emphasis on teaching home food preparers to refrigerate thawed foods within a two‐hour period is an educational priority.     

MECHANISMS UNDERLYING THE ROLE OF FRICTION IN ORAL TEXTURE

The role of friction in food texture sensations are reviewed with the focus on results from our own laboratory, concentrating on texture sensations that are affected by the lubricative properties (e.g., roughness and creaminess), by the viscosity (e.g., melting and thickness) and by the used thickeners (e.g., airiness and heterogeneity). A food's lubricative properties are affected by its fat content, fat droplet size, particle size and shape and thickener. Foods with lower fat contents, larger fat droplets, larger particles and specific thickeners exhibited higher friction while their creaminess and fattiness sensations, associated with good lubrication, are reduced. Roughness and dryness sensations, associated with poor lubrication, are increased. Taste and flavor compounds also affected these texture sensations, albeit via a different mechanism. Specific compounds can affect the lubricative properties of saliva resulting in friction‐related sensations, such as astringency. Astringent compounds interact with proline‐rich proteins in saliva, causing precipitation that may be sensed as discrete particles and/or increased roughness. Alternatively, the compounds may precipitate dead cells and other debris present in saliva. Astringent compounds may also directly affect the surface properties of the oral mucosa.     

EFFECT OF CUCURBITA FICIFOLIA FRUIT EXTRACT ON LIPID PROFILE AND ORAL GLUCOSE TOLERANCE IN STREPTOZOTOCIN-INDUCED DIABETIC RATS

Cucurbita ficifolia ( C. ficifolia ) commonly known as pumpkin is a cultivated plant whose fruit can be used for treating various diseases, one of which is diabetes mellitus. This study was undertaken to investigate the effects of long term feeding of C. ficifolia fruit extract on blood glucose, lipid profiles and the oral glucose tolerance test in streptozotocin (STZ)-induced type 1 diabetic rats. Treatment for 30 days showed a significant decrease in blood glucose, triglyceride, low density lipoprotein and a significant increase in high density lipoprotein level. A significant effect on oral glucose tolerance was also noted. Chronic administration showed an improvement in the oral glucose tolerance curve. These results suggest that C. ficifolia fruit extract exhibits hypoglycemic as well as hypolipidemic effects in the STZ-induced diabetic rats.

PRACTICAL APPLICATIONS

Cucurbita ficifolia , also referred to as pumpkin, is commonly used as a traditional remedy for diabetes in Asia, Africa and South America. The present study investigated the hypoglycemic and hypolipidemic effects of C. ficifolia fruit extract in rats with streptozotocin-induced experimental diabetes. Findings from this study demonstrate that C. ficifolia fruit extract has been shown to have, besides hypoglycemic properties, strong hypolipidemic action on diabetic hypertriglyceridemia and hypercholesterolemia as well. Therefore, consumption of C. ficifolia fruit as a therapeutic diet may be useful in the treatment of diabetes.     

THE VARIATION OF MALT WORT SOLUTION FACTORS WITH EXTRACT CONCENTRATION

A simple method for measuring the variation of solution factors of malt wort with extract concentration is described. Direct measurements are made using worts prepared in a pilot mash-tun. The rate of change of solution factor with excess gravity is found to be-0·488.     

DETERMINATION OF POSSIBLE GENOMIC CHANGES ASSOCIATED WITH DIMORPHISM IN CAMPYLOBACTER JEJUNI

Campylobacter jejuni is a leading cause of human gastroenteritis. Using a tissue culture system, researchers have found that spiral forms of C. jejuni are more pathogenic than coccoid forms of the same strain. The objective of this research was to investigate genomic changes associated with the dimorphism in C. jejuni using pulsed‐field gel electrophoresis (PFGE) and sequencing of flaA gene of C. jejuni isolated from chicken carcasses and human stool samples. C. jejuni isolates were cultured for 18 h (spiral form) and 72 h (coccoid form). PFGE profiles of both forms of C. jejuni showed 100% genetic similarity. For sequence analysis of the flaA gene of C. jejuni, its short‐variable region (SVR) was analyzed. For the two forms of the same isolate, the nucleic‐acid sequences of the SVR of flaA showed 95–100% similarity. It is concluded that morphological dimorphism of C. jejuni was not associated with genetic changes as measured by the mentioned tests.     

THE RHEOLOGICAL CONDITIONS ASSOCIATED WITH JUDGEMENT OF POURABILITY AND SPREADABILITY OF SALAD DRESSINGS

A panel of 25 students compared the pourability and spreadability of two commercial brand salad dressings (non-Newtonian) and a CMC-sugar solution (Newtonian). Correlation of their responses with visco-metric data for the 3 samples indicated that the shear stress and shear rate associated with the sensory evaluation of these two properties are 190–430 dyne cm⁻² and 0.9–6.3 s⁻¹, and < 190 dyne cm⁻² and < 0.9⁻¹, respectively.     

EVALUATION OF TEXTURE OF PECTIN JELLIES WITH THE VOLAND-STEVENS TEXTURE ANALYZER

Texture profile analysis (TPA) parameters were determined with a Voland-Stevens Texture Analyzer-1000 (VSTA) and an Instron Universal Testing Machine. Because of the nature of the design of VSTA, reliable magnitudes of TPA parameters based on the force-time curves recorded during the down stroke can be calculated. With a 2.54 cm diameter plexiglas plunger, the TPA parameters with the VSTA were higher than those with the Instron by 1.45% for hardness to 16.1% for fracturability.     

INFLUENCE OF SUCROSE, GLUCOSE AND LACTOSE ON LOSS OF WATER FROM SOLUTIONS

SUMMARY— Moisture losses from solution of 40, 50, and 60% lactose, sucrose, glucose, and combinations of these sugars were determined at 80°F and 27 in. vacuum. Differences in rate of water loss of 20–50% were observed depending on type of sugar and concentration. Rate of water loss from solution was in ascending order of sucrose, lactose, glucose, and pure water. In mixtures, the rate increased with increased proportion of lactose or glucose, and decreased with increased proportion of sucrose. In all cases, after lactose crystallization occurred, the water loss first increased and then decreased.     

VARIATION IN THE SELENIUM CONTENT OF INDIVIDUAL BRAZIL NUTS

Brazil nuts are high in selenium content relative to other human foods. Since the limits between human selenium essentiality and toxicity are narrow, it is important to know the variation in selenium content of individual nuts. Analysis was performed on 72 individual nuts obtained in stores as shelled nuts in bulk and shelled and unshelled nuts in packages. Their average selenium content was 14.66 ppm with a range of 0.2 to 253.0. The agronomic and health aspects of these findings are discussed.