INCUBATION OF BARLEY KERNEL SECTIONS WITH PURIFIED CELL WALL DEGRADING ENZYMES

The effects of purified Trichoderma reesei endo-xylanase, XYN II and endoglucanases, EG I and EG II on the cell walls of embedded barley cross sections were studied. The cell walls were stained with Calcofluor which is specific for (1–3)(1–4)-β-D-glucans (mixed-linked β-glucans) in histochemical applications. Whereas endosperm cell walls remained highly fluorescent after incubation with buffer, the aleurone cell walls were only weakly fluorescent. Both EG I and EG II were effective in degrading the outer endosperm cell walls, but had little or no effect on the inner endosperm and aleurone cell walls. Corresponding sections incubated with XYN II showed highly intensive fluorescence of aleurone cell walls suggesting that the surface of alaurone cell walls contains a high level of xylan which is removed by xylanase treatment exposing a layer rich in mixed linked β-glucans. This indicates that arabinoxylans and β-glucans in the aleurone cell walls of barley exist as separate, macroscopic layers. Xylanase did not have any Influence on the microstructure of endosperm cell walls which are rich in mixed linked β-glucans. However, incubation with EG II after xylanase treatment caused the aleurone cell walls to become very thin.     

CELL WALL COMPOSITIONS AND ENZYMES OF POTATOES, JICAMAS AND CHINESE WATER CHESTNUTS

Cell wall compositions and the levels of ten enzymes of potatoes, jicamas and Chinese water chestnuts were determined to explain the differences in thermal softening of these vegetables. Cell walls were prepared from the tissues by sieving of ethanolic homogenates to remove most of the starch and analyzed for neutral sugars and uronic acids. Jicamas and water chestnuts contain less galactose but more arabinose and glucuronic acid and much more xylose than potatoes. Water chestnuts contain less galacturonic acid than jicamas and potatoes and this was confirmed by extraction of pectin under various conditions. The results suggest that resistance to thermal softening may be related to cell wall polysaccharides rich in arabinose, glucuronic acid and xylose rather than to pectic polysaccharides. The major differences in enzyme compositions are much higher β-amylase and exopolygalacturonase in jicamas and water chestnuts than in potatoes. Water chestnut exopolygalacturonase is unusually heat-stable, but the relationship of this enzyme or of β-amylase to thermal softening is not clear.     

FACTORS INFLUENCING THE BREAKDOWN OF FRUIT IN STRAWBERRY JAM

Abstract. Structural changes produced in strawberries when made into jam were studied by light microscopy. The results indicated that only the epidermal and vascular tissues retained their structural integrity, whereas the bulk of the cells were collapsed and in some instances ruptured. The extent to which fruit of different cultivars broke down during the jam making process was determined, and an expression representing fruit wholeness was derived. It is concluded that a relationship exists between the extent to which strawberries disintegrate during jam boiling and the density of achenes on the surface of berries of a given size.     

EFFECT OF GAMMA IRRADIATION ON SOFTENING CHANGES AND ENZYME ACTIVITIES DURING RIPENING OF PAPAYA FRUIT

The aim of this work was to study the role of cell wall and ethylene related enzymes to papaya fruit firmness. Irradiation treatment was used as an imposed stress to cause changes in firmness. Physiologically mature papaya fruits were irradiated (500 Gy) and allowed to ripen at 22C and 90% RH. Polygalacturo‐nase (PG), pectinmethylesterase (PME), βgalactosidase, cellulose and 1‐aminocyclopropane‐1‐carboxylate oxidase (ACC‐oxidase) activities were followed during ripening and correlated to changes in firmness, skin and pulp color, respiration and ethylene production. The firmness of irradiated fruits was retained at least 2 days longer than in normal fruits and also had a slower rate of softening. Total soluble solids (d?Brix), cellulase activity and ethylene production were not altered by irradiation treatment. The activity patterns of PG, PME and β‐galactosidase were related to pulp softening and affected by irradiation. ACC‐oxidase activity was influenced by irradiation treatment, but its changes were not temporally related to those in firmness. It was concluded that irradiation had no direct effect on firmness but it acted by altering the ripening induced synthesis of cell wall enzymes, mainly PME.     

THE ADSORPTION OF HOP SUBSTANCES ON THE YEAST CELL WALL

The adsorption of hop substances on to the yeast cell wall, as distinct from the total loss during fermentation, followed the classical pattern of the Freundlich adsorption isotherm with both top and bottom fermentation yeasts. In order to avoid adventitious contamination of the yeasts by hop compounds during head formation, the fermentations were not fully attenuated. The three yeasts adsorbed closely similar proportions of hop substances from fermenting worts of the same composition, but the actual amount differed from one series of fermentations to another. The losses of bitter compounds during the fermentations were only partly accounted for by adsorption on the yeast.     

INFLUENCE OF CELL SIZE AND CELL WALL VOLUME FRACTION ON FAILURE PROPERTIES OF POTATO AND CARROT TISSUE

This article presents the influence of cell size and cell wall volume fraction on the failure parameters of potato tuber and carrot tissue. Confocal scanning laser microscope was used for obtaining images of the cell structure of the tissues. The mean cell face area and the cell wall volume fraction obtained from the images was compared with work to failure, failure stress, failure strain and secant modulus obtained in a compression test of potato and carrot tissue at two strain rates. Bigger cells and less amount of cell wall material weakened the tissue, which was visible as a linear decrease in the parameters: work to failure, failure stress and failure strain. There were differences between potato and carrot in the secant modulus. For carrot, the secant modulus changed with microstructural parameters, whereas for potato, the secant modulus did not depend on these values. The strain rate decreases all the failure properties for potato. For carrot, only the work to failure was affected by the strain rate.     

SOFTENING AND BIOCHEMICAL CHANGES OF SAPOTE MAMEY FRUIT (POUTERIA SAPOTA) AT DIFFERENT DEVELOPMENT AND RIPENING STAGES

We investigated some of the physicochemical and biochemical factors associated with flesh softening of sapote mamey fruit during development and ripening. The activities of pectinmethylesterase (PME), polygalacturonase (PG) and β‐galactosidase (β‐GAL) enzymes were measured in fruits harvested at different development stages, and postharvest in two production seasons. The textural changes were most noticeable at the preclimacteric stage in ripening fruit. The water‐soluble pectin (WSP) increased at a different rate than firmness decreased. No correlation between PG or PME activity and changes in firmness was observed in ripening fruits, though a low correlation was seen between β‐GAL activity and softening in climacteric stage. Greatest loss of firmness occurred in climacteric stage. Fruit pulp softening was not dependent on a single enzyme activity.     

草莓粉非酶褐变的抑制及抗结块性研究

对草莓粉非酶褐变的抑制及抗结块性进行了研究,结果表明：添加适量的亚硫酸氢钠、采用内置干燥剂的阻湿阻氧好的保鲜袋包装、在低温低湿条件下贮藏,对草莓粉非酶褐变具有很好的抑制作用;添加硬脂酸镁1.0%、微晶纤维素0.5%、硅胶0.5%,对草莓粉具有很好的抗结块作用.     

啤酒废酵母综合破壁法提取酵母味素技术

本文研究了高压均质、酶法溶胞、冻融法三种细胞壁破碎法对啤酒废酵母抽提物（酵母味素）的得率、蛋白质的转化率及氨基氮溶出率的影响。实验结果,在适宜的自溶条件下,利用综合破壁法可使酵母抽提物中上述三项指标显著提高。     

THE INFLUENCE OF WORK SOFTENING ON THE VISCOELASTIC PROPERTIES OF BUTTER AND MARGARINE

Abstract Creep compliance-time studies at low stresses give more information about the structural changes in work softened butter and margarine than the Cone Penetrometer. They show that margarine undergoes a greater structural change than butter. Margarine loses most of its instantaneous elasticity in an unrecoverable manner. However, most of the Newtonian viscosity loss is recovered. Butter loses much less of its instantaneous elasticity, and most of what is lost is recovered during aging, but less of the Newtonian viscosity which is lost is recovered. Retardation spectra derived from creep compliance-time curves for both butter and margarine before work softening show a peak at ∼10⁴ sec. In contrast to margarine, butter does not lose this peak when work-softened. For margarine, the peak slowly redevelops during aging and occurs at ∼10² sec. Past interpretation of Cone Penetrometer data has been based on the simplified concept of primary irreversible bonds and secondary reversible bonds, and the changes in their relative proportions during work softening. The present approach avoids the allocation of bond strengths into these arbitrary categories, and is based on the realization that butter and margarine contain a wide range of bond strengths.     

EFFECT OF OZONE ON SOFTENING ENZYMES,SORBATE, PIGMENT AND BACTERIA IN RECYCLED PICKLE BRINE1

ABSTRACT The effects of ozone (O₃) introduced into recycled cucumber pickle brines on cellulase (Cx) and polygalacturonase (PG) activities, potassium sorbate, color and bacteria content were examined. Cx and PG were effectively inactivated by O₃. The amount of O₃ required to inactivate a large range of Cx and PG activities was about 176 to 246 μg/ml of recycled brine that was added in 10–14 min. The O₃ treatments also destroyed potassium sorbate and bacteria in the recycled brines. While being treated with O₃, brine color faded as measured at 400 nm, and after exposure to O₃, the color gradually returned to its original absorbance. Utilization of O₃ provides an alternative method of inactivating Cx and PG in recycled pickle brines; however, the effects of O₃ treated brines on cucumber fermentation and subsequent pickle quality must also be evaluated prior to implementing commercial treatments.     

VARIATION OF CELL WALL CONTENT IN FLOCCULENT AND NON-FLOCCULENT YEAST STRAINS

Estimation of the wall content of a number of flocculent and non-flocculent yeast strains taken in both the growth and stationary phases reveals that flocculent yeasts almost invariably increase their wall content to a greater extent as the cells pass to the stationary phase than do non-flocculent strains. This variation of increase is observed whether the yeasts are grown in hopped wort or in a synthetic malt-yeast-peptone-glucose medium. There are considerable variations in wall content from strain to strain in both types of yeast. Cells of flocculent strains are more difficult to disrupt than those of powdery strains. The nitrogen, phosphate and carbohydrate contents of the walls of all strains varied between the growth and stationary phases but no significant trends were noted in any of the components which could be related to flocculent or non-flocculent behaviour.     

RHEOLOGICAL INDICES OF FRUIT CONTENT IN JAMS: EFFECT OF FORMULATION ON FLOW PLASTICITY OF SHEARED STRAWBERRY AND PEACH JAMS

The effect of formulation factors on Casson yield values measured at low shear rates (0.08 ≤γ≤ 1.01s^-1) (σ₀₁) and at medium shear rates (2.58 ≤γ≤ 387.30s^-1) (σ₀₂) was analyzed in previously sheared strawberry and peach jams. Twenty three samples of each fruit jam were prepared according to a second order composite rotatable design. Composition ranges were: fruit content, 25–55%; soluble solids content, 60–70° Brix; added pectin in strawberry jams, 0.3–0.7% and in peach jams, 0.1–0.5%. Variation of σ₀₁ values in strawberry jams depended mainly on the interactions between fruit and soluble solids and between fruit and pectin, while in peach jams, it depended on fruit-soluble solids and soluble solids-pectin interactions. Patterns of change of σ₀₂ values with composition were similar to those observed for σ₀₁ in both strawberry and peach jams. Predictive power of σ₀₁ and σ₀₂ values for estimation of fruit content was low, but taken in conjunction with soluble solids content and total pectin values, 79.5% of the variability of fruit content in strawberry jams and 91.1% of same in peach jams could be explained.