Atomic force microscopy (AFM) is a type of scanning probe microscopy that generates images (primarily topographical ones) by scanning the surface of samples with a sharp tip. AFM is applicable to samples with low electric conductivities, and its operating range spans that accessible to both light and electron microscopes, allowing for molecular resolution. These features of AFM enable soft materials to be visualized under natural conditions without harsh or damaging procedures. For food polysaccharides, AFM is capable of visualizing not only dispersed molecules but also molecular assemblies with an advantage over other physical techniques in quantifying the heterogeneity of samples. From these perspectives, AFM is one of the most versatile techniques for obtaining structural information on food polysaccharides, contributing to the progress of this research area. In this article, AFM images of various food polysaccharides are presented along with the usefulness and limitations of this microscopy technique.
Microscopic molecular structures govern macroscopic rheological behavior of food polysaccharides in an aqueous system. To understand the macroscopic rheological behavior of polysaccharides on a molecular level, molecular assemblies or supermolecular structures should be investigated because solution or gel properties are indications of molecular associations or network formation. To observe the supermolecular structures, atomic force microscopy (AFM), a type of scanning probe microscopy with the molecular resolution, is one of the most versatile techniques. A series of studies has been carried out using well-characterized polysaccharide samples, including gellan gum and carrageenan, in relation to the structure-function correlation. Molecular understanding is inevitable for the progress of the food industry from both fundamental and application perspectives, leading to the best usage of polysaccharides and to the creation of new texture-based products with high palatability and functionality using polysaccharides.
The viscoelastic properties of Japanese rice porridge were measured using a non-rotational concentric cylinder rheometer. The viscosity and shear modulus of rice porridge exponentially increased with an increase in cooked rice concentration (i.e., 10%, 30%, 50%, 70% and 97% rice porridges). A Mooney's type model can be used to reasonably describe the viscosity of rice porridge as a function of the solid volume fraction. Small rice grains made by polishing and grinding produced low viscosity and shear modulus rice porridges. Moreover, the viscosity and shear modulus of rice porridge increased rapidly after cooking owing to an increase in the rice grain volume with water adsorption.
Various salts can be substituted for sodium chloride (NaCl) to give food a salty taste. In these experiments, a small percentage of total NaCl was replaced by another salt (KCl, MgCl2, CaCl2). The effects of these various salts on the physical strength and water-retention ability of egg sol/gels were investigated. In addition, the saltiness of diluted egg gels and solid cooked rice seasoned by these salt mixtures was evaluated by a large number of individuals. Results showed that substitution of Na by Mg or Ca salt imparted the egg white gels with high breaking stress and strain, and the egg gels showed less water loss by syneresis as compared with gels to which Mg or Ca salt alone had been added. Furthermore, substitution by K or Mg salt was acceptable by taste in egg solution gel and boiled rice, but when Ca was substituted, it was acceptable by taste only in boiled rice.
The inhibitory effects on α-glucosidase (AGH) and the glycemic index (GI) of four lyophilized herbal samples and five herbal tea samples were evaluated in terms of their efficacy for developing therapeutic diets for patients with diabetes. The AGH activity of these samples was evaluated in vitro using an immobilized enzyme (iAGH) that imitated the small intestinal membrane (Kawada et al., 2006). Lyophilized herbal samples, including dill, Italian parsley, corn salad, and rocket, inhibited AGH activity. The GI of the lyophilized samples of Italian parsley, corn salad, rocket, and the raw samples of dill, corn salad, and rocket, was on average less than 100, but not statistically significant. Moreover, all herbal tea samples inhibited AGH activity, and the GI of lemon balm was only slightly reduced, but not statistically significant. In this paper, we discuss the possible application of herbal foods as dietary therapy for patients with type 2 diabetes.
The yeast strain AK 46 was isolated from dough containing fermented cherry fruits and identified as Saccharomyces cerevisiae. The nucleotide sequence of the rDNA spacer region from this strain coincided with those from the yeasts used for the production of whisky, wine, and bread. In a comparison with six baking strains, strain AK 46 possessed less leavening ability in dough with and without addition of 5% sucrose (based on the weight of flour) but a high ability in sweet dough containing 30% sucrose. The activities of the two enzymes α-glucosidase and invertase, which are related to dough fermentation, were lower than those in the other strains. A baking test showed that strain AK 46 was applicable for breadmaking using the straight dough and sponge dough methods. Strain AK 46 carried only SUC2, which is one of multiple genes encoding invertase, in contrast to the other baking strains, and its sequences diverged from those of the corresponding gene from a representative laboratory strain. Southern hybridization of genomic DNA, using the SUC2 gene as the probe, readily discriminated strain AK 46 and other strains. These observations indicate that strain AK 46 is a wild strain possessing breadmaking properties.
Changes in 44 compounds of yuzu (Citrus junos Sieb. ex Tanaka) steam-distilled peel oil (SDO) and possible artifacts that accrue during storage at 25°C were investigated after 1, 2, 3, 4, 8 and 12 weeks. Changes in SDO composition during storage took place more rapidly than in cold-pressed oil. Total monoterpene hydrocarbons decreased markedly, with major losses of limonene and γ-terpinene and notable increases in p-cymene, as well as alcohols. Bicyclogermacrene, the main sesquiterpene hydrocarbon of the fresh oil, practically disappeared. (–)-Spathulenol, the main artifact, was converted from bicyclogermacrene. Antioxidants such as α-tocopherol, β-carotene and 2,6-di-tert-butyl-4-hydroxytoluene (BHT) slowed the formation of oxidation products, such as p-cymene, (–)-spathulenol by inhibiting the formation of oxidative products. This suggests that the antioxidants can be used to maintain yuzu oil quality.
The objective of this study was to establish a new approach that could be used to characterize trace levels of 4-mercapto-4-methyl-2-pentanone (MMP) in Japanese green tea (Sen-cha). MMP included in the headspace of the powdered tea leaf was extracted using a Solid-Phase Microextraction (SPME) fiber, and subsequently, the determination of MMP in Sen-cha was achieved by Gas Chromatography-Mass Spectrometry (GC-MS) with Selected Ion Monitoring (SIM). To efficiently extract MMP from Sen-cha, the effect of the fiber composition, extraction temperature and time, sample amount, solvent and moisture present in the matrix were investigated, and then the optimum extraction conditions were selected. The calibration curve, which was obtained by the standard addition method, for MMP ranging from 0 to 2.0 ppb showed good linearity, and the difference in the matrix was only slightly affected by this analytical procedure. Therefore, this simple and rapid analytical method proved effective in determining trace levels of MMP in various Sen-cha products by the standard addition method using the same slope of the calibration curve. In addition, based on application of this new analytical technique for the characterization of MMP in Sen-cha, the total flavor intensities of Sen-cha were determined to have a close relationship to the amount of MMP, and its amounts were assumed to be dependent on the steaming conditions of the fresh tea leaves during Sen-cha production.
Composite weaning foods using cereals, legumes and vegetables were formulated and analyzed for nutrients, functional properties, sensory attributes and storage stability. Germinated, dried and dehulled legumes, green gram (Phaseolus aureus) and lentil (Lens culinaris) and wheat, rice, carrot and skim milk were mixed in different proportions to get four different formulations, roller dried and analysed for various parameters. The results showed following range of constituents per 100 g of formulation, protein, 18.1-18.9 g; fat, 0.78-1.36 g; iron, 5.09-6.53 mg and calcium, 265-310 mg. Wheat+green gram based food had lowest water absorption capacity whereas rice+lentil based sample had highest. Overall sensory qualities of all four prepared foods were graded as “good” and “very good” with no significant differences. All formulations could be stored for 6 months at room temperature. The results confirm that formulated weaning foods were nutritionally superior, functionally appropriate, microbiologically safe and organoleptically acceptable.
Five apricot (Prunus armeniaca L.) cultivars were examined throughout fruit development period to monitor the changes in quality characteristics including hardness, ºBrix, color, titratable acidity and pH. Changes in the amount of sugars (fructose, glucose and sucrose) and organic acids (citric, malic and quinic) were also determined by HPLC. The predominant sugar of cultivars found to be glucose at the initial ripening stages; however, sucrose or glucose became predominant at the end of fruit maturation. Sugar/ acid rate was found to be the highest in Hasanbey (HB) cultivar during unripe period, while Kabaası (KA) showed the highest value at full ripeness. Low soluble solid containig varieties of Zerdali (ZD) and HB reached fruit maturity earlier than the other cultivars. Soğancı (SO) measured as the hardest fruit at maturity while ZD was the softest cultivar. Chroma as a measure of color, was found to be well corelated with maturity level rather than L value. In the course of ripening, total acid content decreased along with the increasing amount of total sugar for all cultivars.
The present study examined the enzymes responsible for proteolysis of casein in milk. Reversed-phase HPLC was used to differentiate the peptide products, of each proteinase, soluble in 12% trichloroacetic acid and in pH 4.6 milk filtrates. Peptides produced by bacterial proteinase were less hydrophobic and eluted early in the RP-HPLC chromatogram, while peptides produced by plasmin and somatic cell proteinase were more hydrophobic and eluted later. β-caseins were preferential substrates for plasmin, whereas α s-and κ-caseins were hydrolysed to a lesser extent. Proteases from bacterial origin predominantly affected κ-casein, while ß-casein and α s-casein were less susceptible. Somatic cell proteinase degraded mainly β-casein, followed by α s-casein and κ-casein. When milk was contaminated by bacterial proteinases, chromatograms of the TCA 12% filtrate showed early peaks, while the pH 4.6 filtrate showed early and late peaks when proteolysis was caused by either plasmin, somatic cell proteinase or bacterial proteinase.
Characteristics of an exopolysaccharide (EPS) produced by a mutant strain of Lactobacillus plantarum, strain 301102S, including yield from whey, monosaccharide analysis, and prebiotic activity, were investigated. The EPS production in whey was higher at 25°C than at 30 and 37°C. The supplementation with yeast extract and glucose in whey gave a high EPS yield of 145 mg/L, and the EPS contained glucose and mannose (molar ratio, 1:2). Prebiotic activities of galactooligosaccharide, inulin and the EPS with 37 lactic acid bacteria strains were investigated, and prebiotic activity of the EPS was high with the parent strain. This suggests that the EPS produced in whey by the mutant strain is easier utilized by strain 301102 than the other strains, and the EPS produced by this strain is capable for use as a prebiotic.
When brown rice is preserved for a long period of time, a stale flavor (komai-shu) develops as a result of lipid oxidation by enzymes. In order to inactivate the enzymes, brown rice was treated with superheated steam. Superheated steam treatment for about 1 min, at all temperatures, caused a decrease in the enzymatic activity related lipid oxidation. On the other hand, the degree of starch damage did not increase during superheated steam treatment below 150°C. These results show that superheated steam treatment at a low temperature and for a short time is enough to inactivate the enzyme in brown rice, and does not influence starch quality. It was expected that enzyme inactivation by superheated steam treatment would be effective in suppressing the generation of stale flavor during long preservation periods.