A.A. Karim

Methods for the study of starch retrogradation

Abstract The wealth of current knowledge on starch retrogradation is due in large measure to the wide array of analytical methods at the disposal of food scientists. Since retrogradation is a complex process affected by many factors, it is unlikely that any single method would be able to give a complete picture of the retrogradation properties of starch gels at both the macroscopic and molecular levels. Independent evidence derived from two or more methods allows cross comparisons that can provide a fuller understanding of this phenomenon. For quantitative measurement of rates of retrogradation, the “ideal” method should be simple, rapid, non-destructive, precise, and inexpensive. Comparisons of kinetic data from different sources should be made with caution; various factors (thermal history, in particular) that can lead to unjustifiable comparisons and erroneous conclusions should be carefully considered first. This review covers the general principles, capabilities, advantages, and limitations of various methods available to study starch retrogradation.

Sonication improves kasturi lime (Citrus microcarpa) juice quality.

Freshly squeezed kasturi lime fruit juice was sonicated (for 0, 30 and 60min at 20°C, 25kHz frequency) to evaluate its impact on selected physico-chemical and antioxidant properties, such as pH, °Brix, titratable acidity, Hunter color values (L(∗), a(∗), b(∗)), ascorbic acid, DPPH radical scavenging activity, total phenolics, antioxidant capacity, flavonoids and flavonols. Additionally, the effect of sonication treatments on the microbial load (TPC, yeast and mold) were also evaluated. Sonication of juice samples for 60min showed enhancement in most of the bioactive compounds compared to samples treated for 30min and control samples (untreated). Significant reductions in the microbial load corresponding to sonication time were also recorded. Results of the present study indicate that sonication may be employed as a suitable technique for kasturi lime juice processing, where antioxidant and other bioactive compound retention or enhancement is desired, along with the achievement of safety and quality standards.

On the roles of protein and starch in the aging of non-waxy rice flour

Abstract Changes in pasting and thermal properties of non-waxy rice flour and its isolated starch during storage at 25, 35 and 45°C were compared. Aging had no apparent effect on the pasting behaviour of the isolated starch, but markedly affected that of the flour. Peak viscosity ( V p ) of rice flour pastes generally increased with both temperature and time of storage, but reached a plateau within 4 weeks of storage at 45°C. Fresh flour paste exhibited lower V p , a slower rise in apparent viscosity, and much better stability than an isolated starch paste. The addition of isolated oryzenin to isolated rice starch resulted in pasting behaviour which more closely approximated that of an extensively aged flour. DSC scans of fresh flour at ∼13% moisture revealed a weak heat-irreversible endothermic event over the temperature range from 47 to 66°C which was attributed to the denaturation of oryzenin. This transition was shifted to higher temperatures with increasing storage temperature and time. It also became increasingly skewed and broadened until it was no longer detectable after the flour had been stored at 45°C for 8 weeks. Starch gelatinization characteristics of both flour and isolated starch, as determined by DSC, were apparently unaffected by aging. However, rice flour exhibited significantly higher onset temperature of gelatinization, but lower gelatinization enthalpy, than isolated rice starch. Similarly, pulsed NMR studies showed no apparent effect of aging on retrogradation behaviour of rice flour or starch gels. These results suggest that modification of the protein component, rather than starch, was primarily responsible for rheological changes associated with aging of rice flour.

Modification of the microstructural and physical properties of konjac glucomannan-based films by alkali and sodium carboxymethylcellulose

Abstract Edible films were cast from konjac glucomannan (KGM) solutions, with or without added alkali (KOH) and/or sodium carboxymethylcellulose (CMC). Four types of KGM-based films (KGM, KGM–KOH, KGM–CMC and KGM–CMC–KOH) were produced and characterized by scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD), moisture sorption, water vapour permeability (WVP), and tensile tests. Tensile properties were studied as a function of water activity ( a w ) over the range from 0.22 to 0.84. SEM revealed that films, with and without KOH, exhibited cross-sectional lamellar structures running perpendicular and parallel, respectively, to the film surface. Alkali treatment produced films with enhanced crystallinity, lower water-sorptive capacity (WSC) and WVP, and higher tensile properties. These effects were attributed to alkaline deacetylation of KGM molecules which permitted greater intermolecular interactions. The presence of CMC appeared to suppress crystallinity of native KGM films, but enhanced that of deacetylated KGM films. Films incorporating CMC exhibited higher WSC and WVP, but variable tensile properties depending on alkali treatment and a w . The tensile properties of all KGM-based films were profoundly affected by a w . Tensile modulus (TM) of all films were antiplasticized as a w was increased from 0.22 to 0.43, but tensile strength (TS) was generally plasticized by water. Tensile elongation of KGM, KGM–KOH, and KGM–CMC–KOH films was generally much less sensitive to water. However, KGM–CMC films exhibited minimum elongation, attributed to antiplasticization by water, over the intermediate a w range from 0.43 to 0.69. KGM–CMC–KOH films exhibited the highest TM and TS at any particular a w .

Quality attributes of starfruit (Averrhoa carambola L.) juice treated with ultraviolet radiation

Starfruit juice were exposed to ultraviolet (UV-C) light for 0, 30 and 60min at room temperature (25±1°C). On exposure, the titratable acidity significantly decreased, while the decrease in °Brix and pH were not significant. With regard to colorimetric parameters, L(∗) value increased significantly with a subsequent decrease in a(∗) and b(∗) values corresponding to UV treatment time. Except for the ascorbic acid, other antioxidants measured (% DPPH inhibition, total phenols, flavonols, flavonoids and antioxidant capacity) showed enhancement on expsoure to UV (significant at 60min). Microbial studies showed reduction in APC, yeasts and mould counts by 2-log cycle on UV treatments. These results supports the application of UV as a measure of non-thermal and physical food preservation technique for starfruit juice that can be explored commercially to benefit both the producers and consumers.

Effect of carrageenan on yield and properties of tofu

Abstract The effects of the polysaccharide carrageenan and three types of coagulants namely, glucono-δ-lactone (GDL), calcium sulphate (CS) and calcium acetate (CA) on yield and physical properties of tofu (soybean curd), were investigated. Moisture content and yield of GDL-coagulated tofu were higher than that coagulated with CS and CA. Addition of carrageenan did not increase yield of GDL-tofu significantly but increased yield of CS-tofu and CA-tofu by 33 and 46.7%, respectively. Texture of CS-tofu was harder than CA- and GDL-tofu. Carrageenan brought about a significant decrease in hardness of CS- and CA-tofu which was more pronounced at the higher gum concentration. Hardness of GDL-tofu was not significantly altered. The tofu gels exhibited syneresis on storage at 4°C for 24 h in the order: CS-tofu

Effects of Na2CO3 and NaOH on DSC thermal profiles of selected native cereal starches

The effects of Na2CO3 and NaOH (at a concentration of 1 g alkalising agent/100 g dry starch) on the gelatinisation properties of 1:4 and 2:3 starch/water mixtures were studied using differential scanning calorimetry (DSC). The starches studied included wheat, rice, waxy rice, corn and waxy corn. The addition of Na2CO3 or NaOH resulted in significant increases in transition temperatures (onset, peak and conclusion), associated with starch gelatinisation, suggesting a stabilisation of the starch granules, probably through electrostatic interactions between Na+ ions and starch hydroxyl groups. The presence of Na2CO3 generally caused a significant reduction in gelatinisation enthalpy (ΔHG) of the higher moisture (1:4) systems, but had no effect in the less hydrated (2:3) systems. NaOH generally had no effect on ΔHG of 1:4 systems, but gave rise to inconsistent effects in the 2:3 systems. Heating of alkali-containing samples above the gelatinisation temperature range gave rise to an intriguing exothermic peak, the origin of which was attributed to repolymerisation of the products of alkaline hydrolysis of starch. A separate experiment, conducted to investigate the influence of increasing Na2CO3 concentration (up to 3 g/100 g starch) on thermal properties of 1:4 waxy rice starch/water systems, showed a gradual increase in gelatinisation transition temperatures, a general decline in ΔHG, and a marginal decrease in peak temperature of the repolymerisation exotherm.

The free radical scavenging and antioxidant activities of pod and seed extract of Clitoria fairchildiana (Howard)- an underutilized legume.

We evaluated the phenolic content and antioxidant capacities of pod and seed extracts (in methanol, ethanol, and water) of an underutilized legume, Clitoria fairchildiana (Howard). The antioxidant capacity of the extracts was determined using the ferric reducing antioxidant potential assay, and the free radical-scavenging capacity was evaluated using 2,2-diphenyl-1-picrylhydrazyl radical-scavenging and ABTS assays. In addition, the total flavonoids, flavonols, and tannin contents were also determined. Overall, the methanol extracts of the pod contained high concentration of phenolics and showed high antioxidant capacities compared to seed extracts. In addition, a positive correlation was found between total phenol and tannin versus antioxidant capacity. Results of the present study indicate pods and seeds of C. fairchildiana to possess rich amount of natural antioxidants, and can be further explored for their possible use as a natural additive in food or in pharmaceutical industries.

Towards producing novel fish gelatin films by combination treatments of ultraviolet radiation and sugars (ribose and lactose) as cross-linking agents

Developing novel fish gelatin films with better mechanical properties than mammalian gelatin is a challenging but promising endeavor. Studies were undertaken to produce fish gelatin films by combining treatments with different sugars (ribose and lactose) followed ‘by’ ‘and’ ultraviolet (UV) radiation, as possible cross-linking agents. Increase in tensile strength and percent elongation at break was recorded, which was more significant in films without sugars that were exposed to UV radiation. Films with added ribose showed decreased solubility after UV treatment and exhibited higher swelling percentage than films with added lactose, which readily dissolved in water. FTIR spectra of all the films showed identical patterns, which indicated no major changes to have occurred in the functional groups as a result of interaction between gelatin, sugars and UV irradiation. The results of this study could be explored for commercial use, depending on industrial needs for either production of edible films or for food packaging purposes.

Evaluation of Free Radical Scavenging Activity and Antioxidant Potential of a Few Popular Green Leafy Vegetables of Malaysia

In this study, phenolic contents and antioxidant activity of five popular green leafy vegetables of Malaysia—Kangkung, Kucai, Di Huang Miao, Ubi Keledek, and Yaw Mak Choy—were evaluated. Methanol, acetone, and distilled water were the solvent systems used for extraction. The antioxidant capacity of the extracts was evaluated using ferric reducing antioxidant potential assay and the free radical scavenging capacity was evaluated using the DPPH· radical-scavenging assay. The total flavonoids, flavonols, and tannins were also quantified. The efficacy of the three solvents used for extraction differed significantly for both the levels of antioxidants and free radical scavenging activity. In general, methanol was the best of the three solvents for extraction of antioxidants. The results of this study will be useful for health conscious consumers, and they will provide a basis for future exploration of these green leafy vegetables as potential sources of natural antioxidants for food and nutraceutical applications.