Texture of cooked potatoes: Relationship between the compressive strength of cooked potato disks and release of pectic substances

In experiments where the interaction of starch and cell size were kept to a minimum by taking identical material for each experiment (disks from the same tuber), the loss of compressive strength of potato tissue on cooking was found to be related to the release of pectic substances into the cooking liquor. This relationship was found to hold true whether large differences in compressive strength were produced by cooking the disks in water for varying lengths of time or by cooking disks in solutions of calcium or potassium chloride for fixed times. The release of starch into the cooking liquor was not related to loss of compressive strength when the results of a number of experiments from disks from the same tuber were compared. Increased cooking time, or the presence of potassium chloride in the cooking solution, reduced compressive strength and increased the amount of pectic substances released. The presence of calcium chloride had the reverse effect. It was not clear whether the effects of calcium chloride were due to calcium per se or the pH of the solutions after cooking, which were inversely related to calcium chloride concentration.     

Survival of Lactobacillus rhamnosus strains in the upper gastrointestinal tract

In the present study six probiotic Lactobacillus rhamnosus strains were investigated for their ability to survive in the human upper gastrointestinal tract through a dynamic gastric model of digestion. MRS broth was used as delivery vehicle and survival was investigated during in vitro gastric and gastric plus duodenal digestion. Results highlighted that all tested strains showed good survival rate during both gastric and duodenal digestion. In particular, three strains exhibited a great survival showing a recovery percentage in the range between 117 and 276%. In agreement with survival data, high lactic acid production was detected for all strains, confirming their metabolic activity during digestion.     

Enhanced Terahertz Receiver Using a Distributed Bragg Reflector Coupled to a Photoconductive Antenna

We report the use of a terahertz (THz) receiver fabricated using a photoconductive antenna mounted upon a distributed Bragg reflector (DBR). It is shown that the relative performance of the device is in accordance with the reflectivity curves of the DBR. At maximum reflectivity the device improved upon the reference THz signal by up to 30%. In addition, we characterize the saturation of the device with laser pump power and it is shown that the device exhibits an improved optical efficiency when compared to the reference receiver.     

Comparative resistance of food proteins to adult and infant in vitro digestion models

IgE‐mediated allergy to milk and egg is widespread in industrialised countries and mainly affects infants and young children. It may be connected to an incomplete digestion of dietary proteins causing an inappropriate immune response in the gut. In order to study this, a biochemical model of infant gastroduodenal digestion has been developed, which has reduced levels of protease (eightfold for pepsin and tenfold for trypsin and chymotrypsin), phosphatidylcholine and bile salts, compared with the adult model. This model has been used to study the behaviour of three characterised food‐relevant proteins (bovine β‐lactoglobulin (β‐Lg), β‐casein (β‐CN) and hen's egg ovalbumin), all of which are relevant cows' milk and hens' egg allergens. Digestion products were characterised using electrophoresis, immunochemical techniques and MS. These showed that ovalbumin and β‐CN were digested more slowly using the infant model compared with the adult conditions. Resistant fragments of β‐CN were found in the infant model, which correspond to previously identified IgE epitopes. Surprisingly, β‐Lg was more extensively degraded in the infant model compared with the adult one. This difference was attributed to the tenfold reduction in phosphatidylcholine concentration in the infant model limiting the protective effect of this phospholipid on β‐Lg digestion.     

Influence of variety,site and storage on physical,sensory and compositional aspects of mashed potato

Over two seasons, eight potato varieties were grown locally and the three principal UK maincrop varieties at different sites. After periods of storage domestically prepared mashed potato was made from this material and assessed for back extrusion, adhesion, particle and cell size and distribution, ‘free’ starch, dry matter and cell wall polysaccharides in conjunction with sensory textural assessments for mealiness, moisture and structure. The results indicate that there are strong correlations between the physical measurements of work done during back extrusion (EWD) and the deformation to peak adhesion force (ADP) with both dry matter (DM) and the mean sensory scores for mealiness, moisture and structure. The sensory characteristics were also highly interdependent. The r value of these relationships declines after prolonged storage. No significant correlations were found between particle size or cell size and distribution and any of the physical, sensory or compositional data at any storage time. With the three principal UK maincrop varieties, site influenced DM and hence physical and sensory texture more strongly than variety.     

Nutritional composition of UK retail potatoes,both raw and cooked

Over two seasons, four maincrop potato cultivars together with early varieties, were purchased from a range of retail outlets in three principal consumer areas (London, Birmingham and Glasgow). Samples were analysed for moisture, total nitrogen, non-protein nitrogen, fat, carbohydrates (sugars, starch and dietary fibre), vitamins and minerals. Analyses were carried out on both the raw and cooked (boiled, baked, roast and chipped) tubers every 12 weeks. Values for raw and cooked materials were compared with previously published figures, and cultivar, centre and seasonal effects were identified by analysis of variance. Nutrients found to be lower than the Food Composition Table data were riboflavin and niacin (50%), potassium (40%), iron, copper and zinc (20–30%); thiamin and total folate were 2–3 times higher, total ascorbate, initially similar, declined more rapidly after harvest. These differences were reflected in the values obtained for the cooked potato where the major difference was a reduction in the fat content of chips by about 40%. Cooking losses were similar to those in the Food Composition Tables. The main varietal effects were confined to the vitamins. Centre effects showed that potatoes from Glasgow had less ascorbate and dry matter but slightly more free sugars. The only significant seasonal effect was for total ascorbate where the second season was higher than the first.     

HORDEIN POLYPEPTIDE PATTERN IN RELATION TO MALTING QUALITY AND THE VARIETAL IDENTIFICATION OF MALTED BARLEY GRAIN

A procedure is described for the extraction of hordein fractions from single seeds of barley and determination of their polypeptide composition by SDS-PAGE. Varietal differences in the hordein polypeptide pattern occur, and on the basis of this character the 28 varieties which are most widely grown in the U.K. can be divided into 11 groups. Whereas several of these groups contain varieties with similar malting quality, other groups contain both good and poor quality varieties. Examination of pilot scale malts and germinating seeds showed little change in the hordein polypeptide pattern during malting or the early stages of germination. Thus the procedure is suitable for use in the identification of malted grain as well as dry seed.     

A rapid method for determining the carbohydrate component of dietary fibre

A simplified procedure for the determination of the non-starch polysaccharides in foods is described. Starch is removed by treatment with heat-stable α-amylase and resistant starch by treating with dimethyl sulphoxide (DMSO) and amyloglucosidase. Total neutral sugars and uronic acids are then measured colorimetrically in the acid hydrolysates of the starch-free material.The method is more rapid than the complex fractionation procedures (Southgate, 1969; Selvendran et al., 1979; Englyst, 1981) but does not provide a detailed composition. The time per sample compares favourably with the gravimetric assay of Asp et al. (1983) and a direct measure of the carbohydrate content of the dietary fibre fraction is obtained. The results compare favourably with those obtained by the complex method of Englyst et al. (1982). The method is applicable to a range of foods, both raw and cooked, and should have application in the routine analysis of dietary fibre since it is comparatively rapid and does not require complex or expensive equipment.     

Intragastric Oil-in-Water Emulsion Fat Fraction Measured Using Inversion Recovery Echo-Planar Magnetic Resonance Imaging

ABSTRACT: The fat fraction of an oil-in-water emulsion was measured in vitro and in vivo in the gastric lumen using inversion recovery echo-planar magnetic resonance imaging and a non-exchanging, 2-compartment longitudinal relaxation model. This predicted the oil emulsion fat fraction in vitro well (Pearson's R = 0.97). Intragastric measurements in vivo correlated well with nasogastric aspirates taken from the stomachs of 7 healthy human subjects ( R = 0.72). This method has potentially important applications in studying the properties of oil-in-water emulsions and also in assessing the intragastric distribution of fat emulsions in vivo and in correlating physiologic gastric emptying of fat and lipid blood absorption profiles.