Moisture-induced aggregation of alpha-lactalbumin: effects of temperature, cations, and pH

Abstract: Alpha‐lactalbumin is an important dairy protein ingredient, and has been widely used in high‐protein foods such as infant formula and nutritional bars for its nutritional and functional properties. The purpose of this study was to investigate the moisture‐induced aggregation of alpha‐lactalbumin in premixed protein dough model systems, and to illustrate the effects of temperature, cations, and pH on the progress of protein aggregation. Our results suggested that storage temperature was a critical factor for protein aggregation in model systems, and the formation of protein aggregates became faster with increases in storage temperature. Calcium significantly improved the thermal stability of alpha‐lactalbumin and slowed down the formation of protein aggregates. The increases in pH accelerated the aggregation of alpha‐lactalbumin. Our results also suggested that the formation of intermolecular disulfide bonds together with noncovalent interactions are the main mechanisms resulting in the moisture‐induced aggregation of alpha‐lactalbumin in model systems. Practical Application: Alpha‐lactalbumin is an important dairy protein ingredient, and has been widely used in high‐protein foods such as infant formula and nutritional bars for its nutritional and functional properties. Our results suggested low storage temperature, the presence of calcium and low pH condition can make high‐protein food products containing alpha‐lactalbumin more stable.     

Effects of Parity,Bacteriological Status,Stage of Lactation,and Dry Period on N-Acetyl-β-D-Glucosaminidase Activity of Milk and Dry Secretion

Quarter foremilk samples from 61 cows were obtained at 1.5, 3, 21, and 35 wk of lactation and at 7 d after drying off. Measurements for each sample were milk SCC, NAGase activity in the milk and ability of milk to promote phagocytosis of Staphylococcus aureus by polymorphonuclear leukocytes. Milk SCC and NAGase were correlated (r = .62). The NAGase in dry cow secretion was 10-fold higher than in milk. Parity differences in NAGase activity were not significant. There were large stage of lactation trends in NAGase: NAGase activity was high in early lactation, decreased in midlactation, and increased in late lactation and in dry secretion. The increase in activity of the enzyme in milk of first parity cows in late lactation was not as great as in milk of second and third lactation cows. N-Acetyl-β-D-glucosaminidase activity of milk from quarters with intramammary infections was higher than that of milk from quarters free of pathogens.     

Comparison of the properties of Ring,Solo, and Siro core‐spun yarns

In this research, core‐spun yarns with an acrylic sheath fiber and a nylon flat core have been produced on the Ring, SIRO, and Solo spinning systems and the effects of some factors were investigated. The studied factors consist of filament pre‐tension (i.e. 1, 7/5, 10, 15, 50, and 100 g), spinning system (Ring, SIRO, and Solo), and feed position of the core filament in the strands of sheath fibers (six types of feed positions). Also, their physical and mechanical properties, including strength, elongation percentage, abrasion resistance, percentage of coefficient of variation (CV%), and hairiness, were all investigated. Finally, in each stage, the best case was determined. The results show that the quality of the core‐spun yarns produced by the SIRO spinning system is better than that of the Ring and Solo core‐spun yarns.     

Effect of tocopherols,tocotrienols, β-carotene,and chlorophyll on the photo-oxidative stability of red palm oil

Effect of tocols, β-carotene, and chlorophyll on photo-oxidative stability of red palm oil (RPO) were studied. Model systems of triacylglycerols+tocols, triacylglycerols+β-carotene, triacylglycerols +tocols+β-carotene, and triacylglycerols+tocols+β-carotene+chlorophyll were exposed to fluorescent light at intensities of 5,000, 10,000, and 15,000 lux for 7 h at 30±2°C. Changes in concentrations of tocopherols, tocotrienols, β-carotene, chlorophyll, and peroxide values were evaluated every hour. Light intensity accelerated degradation of tocols in the triacylglycerols+tocols system and β-carotene in the triacylglycerols+β-carotene system. Gamma-tocotrienol showed the highest degradation rate and β-carotene was the most sensitive compound to changes in light intensity, indicated by the lowest light intensity coefficient (z_i) value. The presence of tocols and β-carotene together showed protective effects for the photo-oxidative stability of RPO. The presence of chlorophyll increased the rate of photo-oxidation at high light intensities. Interactions between tocols and β-carotene contributed to the photo-oxidative stability of RPO.     

Comparisons of protein, lipid, phenolics, γ-oryzanol, vitamin E, and mineral contents in bran layer of sodium azide-induced red rice mutants

BACKGROUND: The bran part of red rice grain is concentrated with many phytochemicals, including proanthocyanidins, oryzanol and vitamin E, that exert beneficial effects on human health, but it contains low levels of essential minerals such as Fe and Zn. In the present study, the protein, lipid, phytochemicals and mineral contents in bran samples were compared among red rice SA‐586 and its NaN₃‐induced mutants. RESULTS: The plant heights of NaN₃‐induced mutants were decreased. The contents of protein, lipid, total phenolics, total flavonoids, total anthocyanins, total proanthocyanidins, total γ‐oryzanol, total tocopherols and total tocotrienols also varied among the tested mutants. The brans of mutants M‐18, M‐56 and M‐50 contained more proanthocyanidins, γ‐oryzanol, vitamin E than that of SA‐586, respectively. M‐54 accumulated more Fe content (588.7 mg kg^?1 bran dry weight) than SA‐586 (100.1 mg kg^?1 bran dry weight). CONCLUSIONS: The brans of M‐18, M‐50 and M‐56 are good sources of proanthocyanidins, vitamin E and γ‐oryzanol, respectively, while the bran of M‐54 is rich in Fe. Thus these mutants could be used to produce high‐value phytochemicals or Fe byproducts from bran during rice grain milling or as genetic resources for rice improvement programs. Copyright © 2011 Society of Chemical Industry     

Effect of Processing on Phenolic Antioxidants of Fruits,Vegetables, and Grains—A Review

Understanding the influence of processing operations such as drying/dehydration, canning, extrusion, high hydrostatic pressure, pulsed electric field, and ohmic heating on the phytochemicals of fruits, vegetables, and grains is important in retaining the health benefiting properties of these antioxidative compounds in processed food products. Most of the previous investigations in the literature on the antioxidants of fruits, vegetables, and grains have shown that food-processing operations reduced the antioxidants of the processed foods, which is also the usual consumer perception. However, in the last decade some articles in the literature reported that the evaluation of nutritional quality of processed fruits and vegetables not only depend on the quantity of vitamin C but should include analyses of other antioxidant phytochemicals and antioxidant activity. Thermal processing increased the total antioxidant activity of tomato and sweet corn. Most importantly, analysis also depends on the condition, type, and mechanism of antioxidant assays used. This review aims to provide concise information on the influence of various thermal and nonthermal food-processing operations on the stability and kinetics of health beneficial phenolic antioxidants of fruits, vegetables, and grains.     

The effect of dietary supplementation of vitamins C and E on the α-tocopherol content of muscles, liver and kidney, on the stability of lipids, and on certain meat quality parameters of the longissimus dorsi of rabbits

The trial was carried out to investigate the effects of adding to the diet of rabbits vitamin E (40; 300; 500 ppm) and C (0; 500 ppm), on vitamin E deposition in the muscles and organs, on the oxidative stability of muscular lipids, and on various meat quality characteristics. The α-tocopherol content in muscles and organs was roughly doubled by feeding the highest levels of vitamin E; it was also increased by giving 500 ppm of vitamin C, but only in those muscles of rabbits receiving 40 ppm of vitamin E. The α-tocopherol content in tissues was negatively correlated with TBARS values of the longissimus dorsi (LD) at days 6 and 8 post mortem (p.m.). Five hundred parts per million (ppm) of vitamin C increased lipid stability of the LD at both 6 and 8 days p.m., though its effect was significant only with 40 ppm of vitamin E. Moreover, 500 ppm of vitamin C resulted in the lowest L(*) and highest pH values at all p.m. times, when the dietary vitamin E was equal to 40 ppm, and in the highest L(*) and lowest pH values when the vitamin E was equal to 300 ppm. Conversely, weight losses of the LD were the lowest, at days 6 and 8 p.m., in the group fed the highest levels of both vitamins.     

Physical and chemical stability of β-carotene-enriched nanoemulsions: Influence of pH, ionic strength, temperature, and emulsifier type

The enrichment of foods and beverages with carotenoids may reduce the incidences of certain chronic diseases. However, the use of carotenoids in foods is currently limited because of their poor water-solubility, high melting point, low bioavailability, and chemical instability. The potential of utilising oil-in-water (O/W) nanoemulsions stabilised by a globular protein (β-lactoglobulin) for encapsulating and protecting β-carotene was examined. The influence of temperature, pH, ionic strength, and emulsifier type on the physical and chemical stability of β-carotene enriched nanoemulsions was investigated. The rate of colour fading due to β-carotene degradation increased with increasing storage temperature (5-55 °C), was faster at pH 3 than pH 4-8, and was largely independent of ionic strength (0-500 mM of NaCl). β-Lactoglobulin-coated lipid droplets were unstable to aggregation at pH values close to the isoelectric point of the protein (pH 4 and 5), at high ionic strengths (NaCl >200 mM, pH 7), and at elevated storage temperatures (55 °C). β-Carotene degradation was considerably slower in β-lactoglobulin-stabilised nanoemulsions than in Tween 20-stabilised ones. These results provide useful information for facilitating the design of delivery systems to encapsulate and stabilise β-carotene for application within food, beverage, and pharmaceutical products.     

Effect of κ-carrageenan on rheological properties, microstructure, texture and oxidative stability of water-in-oil spreads

The effect of κ-carrageenan concentration (0-7.5 g kg⁻¹) on the rheology, microstructure, texture and oxidative stability of water-in-oil (W/O) spreads (600 g fat kg⁻¹ emulsion) was examined over 60 days storage time. Results showed that increasing the κ-carrageenan concentration to 7.5 g kg⁻¹ significantly increased the viscosity of the aqueous phase (to 42.7 mPa s at 60 °C) resulting in gelation of the aqueous phase on cooling. The microstructure of the spreads was disrupted by higher levels of κ-carrageenan, resulting in a less homogeneous distribution of the aqueous phase. Melt temperature (where tan δ > 1) decreased significantly from 62 to 56.2 °C with increasing κ-carrageenan concentration from 0 to 7.5 g kg⁻¹. The firmness and the G′ at 6 °C for all samples were significantly increased after 60 days storage with only small effects due to κ-carrageenan levels. Oxidation of the fat phase was evident by the significant increases in peroxide values of all spreads on storage, with κ-carrageenan exhibiting no antioxidant behaviour. While increased κ-carrageenan levels modified the microstructure of W/O spreads in terms of the droplet size of the aqueous phase and its distribution few changes were evident in the continuous fat phase.     

Type 2 diabetes-related bioactivities of coffee: Assessment of antioxidant activity,NF-κB inhibition,and stimulation of glucose uptake

Coffee consumption is correlated with a lower risk for type 2 diabetes mellitus (T2D), though whether differences exist in the T2D-mitigating bioactivities of decaffeinated (RD) and regular (RR) coffee is unclear. We conducted cell-based experiments to determine whether different phenolic levels in RD and RR affect T2D-mitigating bioactivities. The total phenolic content and the chemical antioxidant activity were significantly higher in RD than RR. However, these coffees had comparable cellular antioxidant activity. Both coffees reduced activation of NF-κB, with RR being twice as strong as RD. They also both increased glucose uptake in human adipocytes by 2-fold. Of the bioactivities examined, only chemical antioxidant activity was related to total phenolic levels. The NF-κB inhibition was proportional to chlorogenic acid levels, though chlorogenic acids could not account for the full inhibitory effect of coffee. Thus, a matrix effect may exist, whereby components of coffee work together to provide bioactivities that ameliorate the T2D risk.     

Extracts of edible and medicinal plants in inhibition of growth, adherence, and cytotoxin production of Campylobacter jejuni and Campylobacter coli

Abstract: Campylobacter spp. is recognized as one of the most common cause of food‐borne bacterial gastroenteritis in humans. Campylobacter infection causes campylobacteriosis, which can range from asymptomatic to dysentery‐type illnesses with severe complications, such as Guillian‐Barre syndrome. Epidemiological studies have revealed that consumption of poultry products is an important risk factor of this disease. Adherence and cytotoxic activity of the bacteria to host mucosal surfaces have been proposed to be critical steps in pathogenesis. Innovative tools for controlling Campylobacter, such as natural products from plants, represent good alternatives for use in foods or as therapeutic agents. In this study, 28 edible or medicinal plants species were analyzed for their bactericidal effects on the growth of Campylobacter jejuni and C. coli. The extracts of Acacia farnesiana, Artemisia ludoviciana, Opuntia ficus‐indica, and Cynara scolymus were the most effective against these microorganisms at minimal bactericidal concentrations (MBCs) of 0.3, 0.5, 0.4, and 2.0 mg/mL, respectively. No effect on growth was detected with lower concentrations of extract (25%, 50%, or 75% of the MBC) added to the media. The effect of each extract (75% of the MBC) on adherence and cytotoxicity of C. jejuni and C. coli was evaluated in Vero cells. Adherence of Campylobacter to Vero cells was significantly affected by all the extracts. Cytotoxic activity of bacterial cultures was inhibited by A. farnesiana and A. ludoviciana. These plant extracts are potential candidates to be studied for controlling Campylobacter contamination in foods and the diseases associated with this microorganism. Practical Application: Innovative tools for controlling Campylobacter, such as natural products from plants, represent good alternatives for use in foods or as therapeutic agents. The extracts of Acacia farnesiana, Artemisia ludoviciana, Opuntia ficus‐indica, and Cynara scolymus were the most effective against these microorganisms. Adherence and cytotoxic activity of the bacteria to host mucosal surfaces which are critical steps in pathogenesis were decreased by these extracts. Our results point to these plants as potential candidates for the control of Campylobacter contamination in foods, the treatment of the diseases associated with this microorganism, and as feed supplements to reduce on‐farm prevalence of Campylobacter.     

Production,structure–function relationships,mechanisms, and applications of antifreeze peptides

Growth of ice crystals can cause serious problems, such as frozen products deterioration, road damage, energy losses, and safety risks of human beings. Antifreeze peptides (AFPs), a healthy and effective cryoprotectant, have great potential as ice crystal growth inhibitors for a variety of frozen products. In this review, methods and technologies for the production, purification, evaluation, and characterization of AFPs are comprehensively summarized. First, this review describes the preparation of AFPs, including the methods of enzymatic hydrolysis, chemical synthesis, and microbial fermentation. Next, this review introduces the major methods by which to evaluate AFPs’ antifreeze activity, including nanoliter osmometer, differential scanning calorimetry, splat-cooling, the biovaluation model, and novel technology. Moreover, this review presents an overview of the molecular characteristics, structure–function relationships, and action mechanisms of AFPs. Furthermore, advances in the application of AFPs to frozen food, including frozen dough, meat products, fruits, vegetable products, and dairy, are summarized and holistically analyzed. Finally, challenges of AFPs and future perspectives on their use are also discussed. An understanding of the production, structure–function relationships, mechanisms and applications of AFPs provides inspiration for further research into the use of AFPs in food science and food nutrition applications.     

Determination of Color,Antioxidant Activity,and Phenolic Profile of Different Fruit Tissue of Spanish ‘Verde Doncella’ Apple Cultivar

The polyphenolic profile and antioxidant activity of peel, pomace, and juice of ‘Verde Doncella’, a Spanish apple cultivar, is presented. Phenolic profile of the worldwide cultivated ‘Red Delicious’ cultivar was used for comparison. Flavanols, hydroxycinamic acids, flavonols, phloridzin, procyanidin B2, and gallic acid were quantified by HPLC. Larger concentrations of polyphenolics were found in the peel, which is in agreement with the total phenolic content and antioxidant activity (FRAP) values. ‘Verde Doncella’ expressed lower concentrations of flavanols and quercetin derivates in peel, pomace, and juice when compared to ‘Red Delicious’. ‘Verde Doncella’ was richer in p-coumaric acid and procyanidn B2 in the peel.     

Structure,stability, rheology,and texture properties of ε-polylysine-whey protein complexes

ε-Polylysine (ε-PL) is a natural preservative of antimicrobial peptides with broad spectrum and high antibacterial properties. The electrostatic complex delivery system formed by ε-PL and whey protein can be used to maintain the stability of ε-PL and solve the problem of limited application of protein-based food. This work aimed to study the interaction between ε-PL and whey protein by multiple characterization methods. The spectroscopy results showed static quenching type and new stretching of C=O for ε-PL–whey protein complexes. Microstructure studies showed that the combination of ε-PL and whey protein made the structure of the complexes become rough and dense. The interaction between ε-PL and whey protein could improve the stability of the complexes system during storage. Additionally, the interaction affected critical gel temperatures and gel texture properties of complexes with change of whey protein concentration, mass ratio of ε-PL to whey protein, pH value in alkaline solutions, and ion concentration. Overall, this study confirmed the interaction between ε-PL and whey protein, and it will provide a reference for the application of ε-PL in protein food matrix.     

Effects of gelatin origin,bovine-hide and tuna-skin,on the properties of compound gelatin–chitosan films

With the purpose to improve the physico-chemical performance of plain gelatin and chitosan films, compound gelatin–chitosan films were prepared. The effect of the gelatin origin (commercial bovine-hide gelatin and laboratory-made tuna-skin gelatin) on the physico-chemical properties of films was studied. The dynamic viscoelastic properties (elastic modulus G′, viscous modulus, G″ and phase angle) of the film-forming solutions upon cooling and subsequent heating revealed that the interactions between gelatin and chitosan were stronger in the blends made with tuna-skin gelatin than in the blends made with bovine-hide gelatin. As a result, the fish gelatin–chitosan films were more water resistant (∼18% water solubility for tuna vs 30% for bovine) and more deformable (∼68% breaking deformation for tuna vs 11% for bovine) than the bovine gelatin–chitosan films. The breaking strength of gelatin–chitosan films, whatever the gelatin origin, was higher than that of plain gelatin films. Bovine gelatin–chitosan films showed a significant lower water vapour permeability (WVP) than the corresponding plain films, whereas tuna gelatin–chitosan ones were only significantly less permeable than plain chitosan film. Complex gelatin–chitosan films behaved at room temperature as rubbery semicrystalline materials. In spite of gelatin–chitosan interactions, all the chitosan-containing films exhibited antimicrobial activity against Staphylococcus aureus, a relevant food poisoning. Mixing gelatin and chitosan may be a means to improve the physico-chemical performance of gelatin and chitosan plain films, especially when using fish gelatin, without altering the antimicrobial properties.     

Evaluation of Norrish’s Equation for Correlating the Water Activity of Highly Concentrated Solutions of Sugars,Polyols, and Polyethylene Glycols

Norrish’s equation, a_\textw = X_\textw exp( - KX²_\texts )a_{{\text{w}}} = X_{{\text{w}}} \exp {\left( { - KX^{2}_{{\text{s}}} } \right)}, where a _w is water activity, X _w and X _s are molar fractions of water and solute, respectively, and K is the correlating constant, has been widely used to predict a _w of aqueous nonelectrolyte solutions in connection with development of intermediate moisture foods, i.e., food having a _w ≥ 0.85. Present work evaluated the ability of Norrish’s equation to model the water activity of solutions of sugars, polyols, and some polyethylene glycols, in a wide range of concentration, i.e., from low to highly concentrated solutions. For sugar and polyols, a relatively small modification of the “most accepted” literature parameters K allowed the fitting of the data for the wide range of solute concentrations corresponding to a range of a _w from 0.99 to about 0.3 for same solutes. However, a modified Norrish’s model needs to be used to model the behavior of polyethylene glycols 400 and 600 up to water activities as low as 0.5.