To evaluate infrared radiation (IR) blanching in comparison to conventional hot water (HW) blanching in inhibiting the browning and extending the shelf life of pecan kernels, the technology of IR ...blanching at 500–700 W for 90–45 s or HW blanching at 90°C for 60 s, and subsequently drying with hot air at 60, 70, and 80°C, respectively, was used, and then the activities of lipoxidase (LOX) and polyphenol oxidase (PPO), antioxidant capacities, color change, microscopic structure, and the shelf life of kernels were analyzed. Results showed that IR blanching not only significantly decreased the subsequent drying time but also effectively inactivated the activities of LOX and PPO, showing a lower residual activity of 15.74%–40.41% and 16.75%–56.25%, respectively. A higher retention of total phenolics was observed in kernels subjected to IR blanching, from 25.03 ± 0.04 to 29.50 ± 0.96 mg GAE/g compared with HW blanching (14.43 ± 0.07 mg GAE/g). Meanwhile, IR‐blanched samples showed lower peroxide values, p‐anisidine values, total color difference values, browning index, quinones contents, and lipofuscin‐like pigments levels but had higher 2,2‐diphenyl‐1‐picrylhydrazyl inhibition rate and better storage stabilities than HW‐blanched samples. The technology of IR blanching at 600 W for 60 s followed by drying with hot air at 70°C for 40 min is suitable for producing pecan kernels with better qualities and a longer shelf life, through inactivating the endogenous enzymatic reactions and inhibiting the formation of lipofuscin‐like pigments.
Practical Application
Blanching is an essential pretreatment of food processing. Conventional blanching is achieved by hot water, which has some disadvantages of low‐intensity enzyme inactivation, loss of water‐soluble substances, etc. In this study, the potential of using infrared blanching, prior to drying, was studied to find solutions to improve the nutritional value, and the shelf life of pecan kernels. The results showed that infrared blanching at 600 W for 60 s followed by drying with hot air at 70°C for 40 min could inhibit the color degradation, improve the oxidation resistance, and prolong the shelf life of kernels.
To improve tofu quality, the effects of using 0.12–0.18 g/100 mL citric acid, l-(-)-malic acid, or tartaric acid as coagulation agents were investigated. The results showed that storage modulus, ...hardness, water-holding capacity, non-freezable water content, and in-gel hydrophobic interactions were optimal when tofu was prepared with 0.14 g/100 mL organic acids, but deteriorated when more than 0.16 g/100 mL was used. Slower acidification during gelling in the presence of 0.14 g/100 mL organic acid promoted protein–protein hydrophobic interactions, resulting in a higher elastic modulus. Moreover, the tofu products showed higher water-holding capacity and non-freezable water content, as well as more compact gel microstructures. Notably, tofu prepared with citric or l-(-)-malic acid was of better quality than tofu prepared with tartaric acid. Collectively, the results demonstrate that soft or firm tofu with desirable physicochemical properties can be prepared with organic acids if acidification is adequately controlled during gelation.
•Acidification rate during coagulation critically impacts tofu quality.•Gentler acidification promotes hydrophobic interactions.•Stronger hydrophobic interactions increase non-freezable water content.•Stronger hydrophobic interactions also improve tofu texture.•Stronger protein-protein interactions generate a more compact tofu microstructure.
•Soy protein isolate (SPI) and wheat gluten (WG) exhibit poor individual gelation.•Ultrasonic pretreatment improved MTGase-induced SPI/WG mixture gelation properties.•Ultrasonic treatment reduced the ...particle size of SPI/WG molecules.•Ultrasonic treatment increased SPI/WG gel water holding capability and gel strength.•SPI/WG gel had denser, more homogeneous protein networks after ultrasonic treatment.
Soy protein isolate (SPI) and wheat gluten (WG) are widely used in commercial food applications in Asia for their nutritional value and functional properties. However, individually each exhibits poor gelation. In this study, we examined the microbial transglutaminase (MTGase)-induced gelation properties of SPI and WG mixtures with high intensity ultrasonic pretreatment. Ultrasonic treatment reduced the particle size of SPI/WG molecules, which led to improvements in surface hydrophobicity (Ho) and free sulfhydryl (SH) group content. However, MTGase crosslinking facilitated the formation of disulfide bonds, markedly decreasing the content of free SH groups. Ultrasonic treatment improved the gel strength, water holding capacity, and storage modulus and resulted in denser and more homogeneous networks of MTGase-induced SPI/WG gels. In addition, ultrasonic treatment changed the secondary structure of the gel samples as determined by Fourier transform infrared spectroscopic analysis, with a reduction in α-helices and β-turns and an increase in β-sheets and random coils. Thus, ultrasound is useful in facilitating the gelation properties of MTGase-induced SPI/WG gels and might expand their utilization in the food protein gelation industry.
Camellia-oil based oleogels were structured at a constant tea polyphenol-palmitate (Tp-palmitate) particles concentration of 2.5% (m/v) and varying citrus pectin concentration of 1.5, 2.5, 3.5 and ...4.5% (m/v) using emulsion-templated method. Optical and laser confocal microscope were used to observe the microstructure of emulsions, dried products formed by freeze-drying the emulsions, and oleogels obtained by further shearing the dried products. Series of rheological measurements were performed to evaluate effects of citrus pectin concentration on the gel strength of emulsions and oleogels. The texture of dried products, and the oil binding capacity, oxidative stability and potential application of oleogels were characterized, respectively. Results revealed that citrus pectin concentration had significant effects on the physical properties of emulsions, dried products and oleogels due to the reinforcement from the interactions and entanglements of polymer. With the increase in the citrus pectin concentration, the stability and viscoelasticity of the emulsions increased, the hardness of the dried products with more compact structure became larger, and the oil binding capacity and gel strength of the oleogels enhanced. Oleogels displayed a high gel strength of G′ > 17,000 Pa and a good thixotropic recovery when the citrus pectin concentration was higher 1.5% (m/v). The polyphenol-rich oleogels had high anti-oxidative activity. The hedonic score in overall quality of cakes prepared with oleogels replacement of butter and that of cakes with butter were 21.49–27.58 and 32.03, respectively. This research gave a reference for preparing oleogels with food-approved polymer and provided more information for their potential application as substitution of solid fats.
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•Camellia oil-based oleogels were formed with an emulsion-templated method.•Tp-palmitate particles and HM citrus pectin were used to structure oleogels.•Stable emulsion, hard dried product and high gel strength oleogel were depicted.•The anti-oxidative oleogels can partially replace solid fats for cakes production.
Summary
To elucidate the effects of salts on the properties of citric acid‐induced tofu gel, gelation was induced in the presence of KCl, CaCl2 or CaSO4, and gypsum tofu was used as a reference. The ...textural properties, water‐holding capacity (WHC), rheological behaviour, aggregate size distribution and microstructure of the tofu were evaluated. The results indicated that the addition of 0.10 g/100 mL KCl,0.05 g/100 mL CaCl2 and 0.15 g/100 mL CaSO4 yields more elastic tofu with high water‐holding capacity. The WHC of tofu induced in the presence of salts was similar to that of gypsum tofu, while the tofu was firmer and less elastic than gypsum tofu. The maximum elasticity of citric acid‐induced tofu was obtained with addition of 0.15 g/100 mL CaSO4. These results are useful to understand the effects of different salts on soymilk gelation and provide a theoretical base for the quality improvement of citric acid‐induced tofu.
The gelation process of tofu induced by citric acid and different salts.
In this study, we elucidated the microbial transglutaminase-induced gelation properties and thermal gelling ability of soy protein isolate (SPI) and wheat gluten (WG) mixture following ultrahigh ...pressure (UHP, 100–400 MPa) pretreatment. UHP treatment induced unfolding and aggregation within SPI/WG protein molecules, which led to increases in free sulfhydryl group content and surface hydrophobicity. However, the transglutaminase cross-linking reaction facilitated the formation of hydrophobic interactions and disulfide bonds and thus resulted in higher gel strength, water holding capacity, and denser and more homogeneous gel networks of transglutaminase cross-linked SPI/WG gels. Rheological measurements revealed that the addition of UHP steps might generate a higher storage modulus (
G
′) value of MTGase-induced SPI/WG gelation during the heating-cooling cycle (25 °C → 95 °C → 25 °C). Our results indicated that various chemical interactions including covalent interactions (i.e., ε-(γ-glutamyl)lysine bonds and disulfide bonds) and non-covalent interactions (i.e., electrostatic forces and hydrophobic interactions) were involved in SPI/WG gel network structures. Hydrophobic interactions and disulfide bonds are significantly increased with the pressure level (100–400 MPa) compared with that of the unpressurized control. Furthermore, UHP treatment reduced the α-helix and β-turn content but increased the β-sheet and random coil structures. Thus, UHP treatment may be considered as a novel technique to expand the utilization of SPI/WG mixture in the food protein gelation industry.
•Tea polyphenol palmitate particles effectively stabilize water-in-oil emulsions.•Stable gel-like water-in-oil emulsions were fabricated and characterized.•Solid camellia oil emulsions were prepared ...using tea polyphenol palmitate firstly.•Water-in-oil emulsions with high slip melting point can be used as a solid fat replacer.
Water-in-oil (W/O) emulsions with a discontinuous aqueous phase dispersed in a continuous camellia oil phase were prepared by using tea polyphenol palmitate (Tp-palmitate) particle as effective stabilizers and their properties were characterized by droplet size, slip melting point (SMP), stability, microstructure and rheology. The d(4,3) and d(3,2) decreased from 7.96 μm to 4.67 μm and from 5.98 μm to 3.07 μm, respectively, and the SMP rose from 33.73 °C to 38.60 °C when the Tp-palmitate concentration increased from 1.0% to 2.5% (m/v). The storage stability, freeze/thaw stability and thermal stability significantly enhanced and the droplets aggregation progressively increased with the increasing of Tp-palmitate concentration. The liquid camellia oil was transformed into solid-like viscoelastic emulsion gels with a SMP of 38.6 °C when using 2.5% Tp-palmitate as particle stabilizers. This study provides a promising method for production of edible gel-like W/O emulsions using polyphenol-lipid complexes to potentially replace solid fats.
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