Volume 14, Issue 4 -

Oyster protein isolate (OPI) suspensions (6.19 % ± 0.82 %, w/v) were treated by high-pressure homogenization (HPH) at 0 (control), 20, 40, 60, 80 or 100 MPa for three cycles. Protein profiles, secondary structure, free sulfhydryl, surface hydrophobicity, particle size distribution, zeta-potential, solubility, water and oil holding capacity (OHC), emulsifying and foaming properties of the obtained suspensions were analyzed. The results showed that HPH treatment did not cause changes in protein profiles of OPI, but caused changes in secondary structure, content of α-helix decreased but content of β-turn and random coil increased significantly ( P < 0.05). Free sulfhydryl and surface hydrophobicity all increased significantly ( P < 0.05) after HPH treatment, indicating that tertiary and quaternary structures changed. Functional properties of OPI significantly ( P < 0.05) improved after HPH treatment, such as zeta-potential (from −12.67 to −33.57 mV), solubility (from 20.24 % to 57.99 %), OHC (from 981.77 % to 1229.40 %), foaming ability (from 17.50 % to 35.00 %), foaming stability (from 44.49 % to 66.60 %), emulsifying activity index (from 8.87 to 17.06 m 2 /g) and emulsion stability index (from 14.65 to 41.68 min). At 60 MPa and 80 MPa, the improvements were more remarkable. However, HPH treatment significantly ( P < 0.05) decreased particle size (from 200–500 nm to 0–200 nm) and water holding capacity (from 341.15 % to 216.96 %). These improvements were closely related to structural changes and reduction of particle size. Application of different pressures affected functional properties of OPI. These results could provide information for determining HPH applying condition in OPI modification.

Commercial agar used in microbiological culture has a disadvantage of impurity and opacity. This work aimed to provide an alternative gelling agent to agar and the function of low acyl gellan gum in microbiological culture media was studied. The results showed the texture and water activity of GYGs (glucose-YNB medium containing low acyl gellan gum at different concentrations of 0.3%, 0.6%, 0.9%, 1.2%, 1.5%) were suitable for cultivation of Saccharomyces yeasts. The gelling temperature of GYGs was enhanced with the increased concentration of low acyl gellan gum, while clarity of medium and colony diameter decreased. Scanning electron microscope showed that GYG09 (glucose-YNB medium containing 0.9% low acyl gellan gum) possessed homogeneous porous structures, which was superior to GYA20 with respect to higher clarity and lower dosage of gelling agent when surface plating method was used; however, GYG09 was not suitable for pour plating method.

Mung bean sprouts are a kind of favorite healthy food across the world. As a forbidden plant hormone cytokinins, the use of 6-benzylaminopurine (6-BAP) in promoting the growth of bean sprouts is forbidden due to its safety concerns. Rapid analysis of 6-BAP treated bean sprouts is required to assess their growth changes and discriminate them from the normal sample. In this study, the water dynamics of growth for 6-BAP treated bean sprouts was monitored by the low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging. A simplified cartoon model of the water dynamics was proposed to explain the LF-NMR analysis result. Principal component analysis of the NMR relaxation data clearly showed the different water distribution of 6-BAP treated bean sprouts from the control sample. The juice of 6-BAP treated bean sprouts showed significant difference in the ultraviolet absorption and fluorescence spectra. Therefore, combining the spectrometry, the LF-NMR may have potential for rapid discrimination of the 6-BAP treated bean sprouts.

In distillation of crude spirits, alcohol content gradually reduces. At varying alcohol contents, trace element types and contents differ in crude spirits. In this study, three samples with 72.7, 65.3 and 55.8 %vol were obtained according to distilled liquor order. Crude spirit samples were analysed every 3 months, with detection of contents lasting for 2.5 years. Primary aldehydes, alcohols and esters were analysed by gas chromatography. Results of this study indicate that higher alcohol content in crude spirits results in higher amounts of aldehydes, alcohol and ester and lower acid content. During storage period of 2.5 years, alcohol contents changed minimally, and varied changes were observed for aldehydes, trends of different acids and esters.

This study investigated the chemical, wettability, thermal and structural properties of starch nanocrystals (SNCs) modified through crosslinking modification using citric acid in aqueous medium. The results of Fourier transform infrared spectroscopy analysis suggested that new interactions occurred between starch and citric acid after modification and an increase of the reaction time increased the degree of substitution. X-ray diffraction analysis showed that the crystalline structure of SNCs was maintained after the crosslinking modification by adjusting the pH to 3.5, and destroyed after the modification by pretreatments without adjusting the pH of the citric acid solution. Crosslinking modification decreased the size and aggregation of SNCs and longer reaction time gave rise to the smaller particle size of SNCs modified by the pretreatments of adjusting the pH of the citric acid solution. The crosslinked SNCs had lower polarity and showed stronger hydrophobicity and dispersion stability which allowed them be used as reinforcements in hydrophobic polymer matrices.

Fouling on heat exchanger surface is a severe problem in food industry. This study investigated the fouling and cleaning behaviors of soy protein isolates (SPI) in heat exchangers, using a previously established real-time monitoring laboratory system. SPI fouling deposit was formed at different surface temperatures of 80, 85 and 90 °C. For cleaning, the effect of the NaOH concentration was investigated. The fouling and cleaning behaviors of whey protein concentrate (WPC) were studied for a qualitative comparison. The two solution concentrations were kept at 6 wt%. Under the constant heat flux condition applied in the experiments, increasing the surface temperature significantly increased the fouling rate of SPI. SPI deposit was much easier to remove compared to WPC deposit. Visualization showed that the cleaning behavior of SPI was different from that of WPC in that it swelled rather quickly followed by the species seeping out from the swollen structure.

Because of its biodegradable trait, starch has been widely used as the raw material for packaging. Effects of different thermal treatment methods (high temperature-high pressure heating (HH), microwave heating (MH) and alkali heating (AH) with and without glycerol on physical properties of high amylose maize starch films (HASFs) were investigated in this study. HASFs under HH had highest elongation at break (E%), and lowest tensile strength (TS), modulus of elasticity (EM) and opacity (OC). HASFs under MH had highest TS, water holding capacity (WHC) and OC, and lowest thickness (TN), E%, solubility in water (SW) and solubility in oil (SO), while HASFs under AH had highest TN, EM, SW and SO, and lowest WHC. Compared with water, plasticized HASFs with glycerol had higher TN，E%, WHC, SW and OC, and lower TS, EM and SO. XRD results revealed the V-type polymorph and the difference in intensity of diffraction peaks of HASFs under three methods. This study would be helpful to design and prepare HASFs.

Seaweed contained health functional polysaccharides and polyphenols. Five extracts were prepared from red seaweed Melanothamnus somalensis ; two of these were aqueous at 20°C (F1) and 70°C (F2), followed by acid (F3), alkali (F4) and acid-washed (F5) treatments. Molecular characteristics of extracts were measured by high-performance liquid chromatography and Fourier transform infrared (FTIR) analyses. Health functionality was determined by sulfate and polyphenol contents, and thermal characteristics were determined by modulated differential scanning calorimetry. Extract F3 contained the highest levels of sulfate followed by F2, F1, F4 and F5, respectively. Similarly, F3 contained the highest polyphenol followed by F4, F2, F1 and F5, respectively. Molecular weight distribution of F1 showed wider distribution of sizes (MW: 1.0 × 10 3 – 3.0 × 10 7 ), and F5 showed a sharp peak (MW: 3.1 × 10 3 ); whereas F2, F3 and F4 indicated bimodal distribution. FTIR indicated that all fractions contained agar except F5 and sulfate ester group was attached to carbon 6 of the saccharide.