Thermal and mechanical behavior of laminated protein films

The whey protein and zein films plasticized by glycerol and olive oil were prepared by casting method and then were laminated. The thermal behavior of the whey protein, zein and whey protein-zein laminated films was investigated by the dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC). Both techniques showed that the films containing olive oil had higher glass transition temperature (T_g) than the films containing glycerol (e.g.115 and 88 °C in the zein-olive oil and zein-glycerol films, respectively). As well as, the laminated films had higher T_g than the whey protein films (e.g.82 and 31 °C in the whey-zein-glycerol and whey-glycerol films, respectively). The T_g values obtained from two different methods were close. The results showed that the T_gs of the zein-glycerol films predicted by Couchman and Karasz equation were very close to the values obtained by DSC experiments. The tensile tests showed that the laminated films had higher tensile strength than the single whey protein films and the single zein films plasticized by olive oil (260% and 200% in the whey-zein-glycerol and whey zein-olive oil films in comparison to single whey-glycerol films, respectively).     

Thermal degradation kinetics of aqueous anthocyanins and visual color of purple corn (Zea mays L.) cob

Purple corn cob was the byproduct during the corn processing. Thermal degradation kinetics and Hunter color parameters (a, b, C, h° and ΔE) of aqueous anthocyanins from purple corn cob were studied at selected temperatures (70 °C, 80 °C and 90 °C) at pH 4.0. The results indicated that the thermal degradation of anthocyanin and Hunter color C, a and ΔE parameters followed the first-order reaction kinetics, while Hunter color h° and b parameters followed zero-order reaction kinetics. The calculated values of activation energies (Ea) were 18.3, 35.9, 37.1, 31.6, 34.9 and 30.0 kJ/mol for anthocyanins, C, a, ΔE, h° and b parameters, respectively. The higher Ea indicated that greater temperature sensitivity of visual color as compared to anthocyanins content. The degradation of anthocyanins showed positive correlation with C (R² > 0.909), a (R² > 0.860) and ΔE (R² > 0.940), while the degradation of anthocyanins showed negative correlation with h° (R² > 0.828) and b (R² > 0.735) during heating.

Industrial relevance

Purple corn cob was the byproduct during the corn processing. Purple corn cob is dark purple to almost black color due to its high content of anthocyanins, which makes this byproduct a good source of anthocyanins. In this study, the excellent linear correlation between Hunter color parameters (a, b, C, h° and ΔE) and content of anthocyanins showed that the Hunter color parameters may also be used instead of anthocyanins content during heating. The advantage of using the visual Hunter color parameters may be measured as on-line quality control parameters during thermal processing of food industry.     

Quality evaluation of raw ground almond kernels (Prunus dulcis): Effect of active and modified atmosphere packaging, container oxygen barrier and storage conditions

The present study investigated the effect of active and modified atmosphere packaging, container oxygen barrier and storage conditions on quality retention of raw ground almonds. Ground almond kernels were packaged in: a) polyethylene terephthalate//low density polyethylene (PET//LDPE), and b) low density polyethylene/ethylene vinyl alcohol/low density polyethylene (LDPE/EVOH/LDPE), under N₂ or with an oxygen absorber and stored either under fluorescent light or in the dark at 4 or 20 °C for a period of 12 months. Quality parameters monitored were: peroxide value (PV), hexanal content, color, fatty acid composition and volatile compounds. Of the sensory attributes color, texture, odor and taste were evaluated. PV ranged between 0.26 for fresh almonds and 19.98 meq O₂/kg oil for almonds packaged in PET//LDPE pouches under N₂ exposed to light at 20 °C after 12 months of storage. Respective values for hexanal were < 28.5 µg/kg and 9.38 mg/kg. Polyunsaturated fatty acids (PUFA) and saturated fatty acids (SFA) increased with a parallel decrease of monounsaturated fatty acids (MFA) after 12 months of storage in samples stored with the oxygen absorber while in samples packaged in PET//LDPE under N₂, a decrease in PUFA and MUFA with a parallel increase in SFA was recorded. Likewise, volatile compounds such as aldehydes, ketones, alcohols, acids, alkanes and aromatic hydrocarbons increased during storage indicating enhanced lipid oxidation. Color parameters L, a and b remained unaffected in all treatments including the oxygen absorber while under a N₂ atmosphere L parameter showed a small but statistically significant (p < 0.05) decrease with a parallel increase (p < 0.05) of a and b values after 12 months of storage. The most pronounced color changes occurred for samples in PET//LDPE pouches irrespective of lighting conditions at 20 °C. Raw ground almonds retained acceptable quality for ca. 6–7 months packaged in PET//LDPE and ca. 8 months packaged in LDPE/EVOH/LDPE pouches under N₂ irrespective of lighting conditions at 20 °C while at 4 °C shelf life was extended by an additional month as compared to storage at 20 °C. Use of the oxygen absorber provided a shelf life of at least 12 months for all samples irrespective of container oxygen barrier, lighting conditions and storage temperature.

Industrial relevance

The use of oxygen absorbers is very effective in extending the shelf life of ground almonds commercially for at least 12 months irrespective of packaging material barrier to O₂, lighting conditions and storage temperature.     

Impact of cooling rates on the staling behavior of cooked rice during storage

The impact of cooling rates (0.40, 1.11, 1.42, 1.64, 2.47 and 3.36 °C/min) on starch retrogradation and textural properties of cooked rice was evaluated. The relationship between cooling rates and different properties were determined using Pearson correlation. Starch retrogradation enthalpy (ΔH_r) of cooked rice was determined by differential scanning calorimetry, and textural properties were determined by a Texture Analyser. This study showed that the ΔH_r value and hardness value had a negative correlation with cooling rate during storage, −0.963  r  −0.716, P < 0.01; −0.826  r  −0.706, P < 0.05, respectively. However, a positive correlation was found between adhesiveness and cooling rate (0.237  r  0.882, P < 0.05). These results indicated that the cooked rice chilled with slower cooling rate retrograded faster than chilled with rapid cooling rate. Therefore, high quality cooked rice can be produced by rapid cooling process.     

Water soluble inner aqueous phase markers as indicators of the encapsulation properties of water-in-oil-in-water emulsions stabilized with sodium caseinate

The aim of this study was to evaluate the suitability of Methylene Blue (MB) and Vitamin B₁₂ (Vit-B₁₂) as water soluble inner aqueous phase (W₁) markers for measuring the encapsulation efficiency and stability of water-in-oil-in-water (W₁/O/W₂) double emulsions stabilized by sodium caseinate (NaCN). The encapsulation efficiency and stability were determined by centrifugation of the double emulsion to separate the cream phase (W₁/O) and the outer aqueous phase (W₂) and measuring the concentration of marker in W₂ by absorbance spectrophotometry. To validate this method the marker concentration measurable and the stability of the marker in W₂ were measured. Both markers could be accurately measured in W₂ and there was no change in the concentration of marker on storage of a W₂ solution for 7 days at 45 °C. The recovery yields of MB and Vit-B₁₂ in the recovered W₂ of an oil-in-water (O/W₂) emulsion, determined using the procedure normally used for measuring encapsulation efficiency and stability, were 78% and 99%, respectively, and 52 and 100%, respectively. Double emulsions had encapsulation efficiency of 61.9 ± 21.4% and 16.6 ± 1.1% and encapsulation stability of 62.0 ± 22.6% and 10.7 ± 0.7% for MB and Vit-B₁₂, respectively. Recovery yield and encapsulation efficiency/stability data for MB indicate that it is not a suitable marker for measuring the encapsulation properties of NaCN stabilized double emulsions while similar data for Vit-B₁₂ indicate that it is a suitable marker for studying the encapsulation properties of double emulsions stabilized with NaCN. Methods used in other studies to measure encapsulation properties of double emulsions are discussed in light of the results obtained in this study.     

Physicochemical changes in whey protein concentrate texturized by reactive supercritical fluid extrusion

The mechanisms of interactions in whey protein concentrate (WPC) texturized by reactive supercritical fluid extrusion and pH modifications were evaluated in terms of protein solubility in different extraction buffers, electrophoresis, free sulfhydryl (SH) groups, and apparent viscosity. The soluble protein content and free SH groups of the texturized WPC (tWPC) produced at pH 2.89 decreased by 20% and 16% relative to the unextruded control. It was completely soluble in the presence of urea and SDS, indicating the importance of non-covalent interactions in maintaining the structure of this product. Its dispersion (20% w/w) yielded a creamy texture with a particle size in the micron-range (mean diameter 5 μm) and contributed 258 times higher viscosity compared to the unextruded control. The tWPC produced at pH 8.16 was soluble only in the presence of a reducing agent. It yielded a grainy texture with a high proportion of large particles due to an extensive aggregation via intermolecular disulfide formations.     

Competitive amino acid transport between -tryptophan and other amino acids in Schizophyllum commune

In our study on nutritional requirement for the hyphal growth of Schizophyllum commune, we found that a Trp⁻ mutant could not grow in the -Trp-supplied medium in the presence of -Ser. Further growth studies showed that not only -Ser but also as many as 11 kinds of amino acid including -Ala, -Arg, -Asn, -His, -Leu, -Met, -Phe, -Ser, -Thr, -Tyr and -Val inhibited the growth of the Trp⁻ mutant in the -Trp-supplied medium. However, these amino acids did not inhibit the growth of a Trp⁺ strain. The inhibition of growth of Trp⁺ strain induced by a Trp analogue of 5-fluoro- -tryptophan (5FT), which was usually recovered by -Trp, was rescued by the same amino acids mentioned above. The exceptions were Gly and -Ile, which also recovered the growth inhibition induced by 5FT. These results indicate that the permease responsible for the Trp transport in S. commune might also be active to other amino acids. However, it is considered that the permease shows high affinity to -Trp and low affinity to other amino acids. As a result, the transport of -Trp and 5FT may be counteracted by other amino acids.     

Kinetics of phase separation during pressure-induced gelation of a whey protein isolate

The kinetic process of pressure-induced gelation of whey protein isolate (WPI) solutions (20–28%, w/v) was studied using in situ light scattering. The gelation of WPI solutions could be induced by pressurization at 250 MPa, a pressure lower than that reported in other studies. The gelation time decreased with increasing WPI concentration and followed an exponential rule. The relationship of the logarithm of scattered light intensity (I) versus time (t) was linear after the induced time and could be described by the Cahn–Hilliard linear theory. With increasing time, the scattered intensity deviated from the exponential relationship, and the time evolution of the scattered light intensity maximum I_m and the corresponding wavenumber q_m could be described in terms of the power-law relationship as I_m  t^β and q_m  t^−α, respectively. These results indicated that phase separation occurred during the gelation of WPI solutions under high pressure.     

Total phenolic compounds and antioxidant capacities of major fruits from Ecuador

Seventeen fruits from Ecuador were analysed for total soluble phenolic compounds content and for antioxidant capacity, using three different methods (DPPH, FRAP and ABTS⁺). For the total phenolic content measured by the Folin–Ciocalteu method, three groups, having <100, 200–500 and >1000 mg GAE/100 g FW, were clearly distinguishable. Andean blackberry, capulí cherry peel and banana passion fruit were classified in the third group, with concentrations of 2167, 1494 and 1010 mg of GAE/100 g FW, respectively. Antioxidant capacity analyses revealed the same classes. FRAP and ABTS⁺ gave comparable results and were highly correlated (y = 0.691x + 6.78; r² = 0.908). Spectrophotometric measurements showed that the Andean blackberry and capulí peel but not banana passion fruit contained high levels of anthocyanins (λ_max = 520 nm).     

Comparison of sucrose and fructo-oligosaccharides as osmotic agents in apple

Fructo-oligosaccharides and sucrose were compared as osmotic agents in the osmotic dehydration of apple cv. Idared. Dehydration process of apple cubes (10  10  10 mm) was performed to determine the weight reduction (WR), moisture content (MC), water loss (WL) and solid gain (SG) over a range of osmotic solutions (40–60% w/v), temperature (40–60 °C) and processing time (20–40 min) The effective diffusion coefficient of water and solute was calculated assuming the processes to be governed by Fick's unsteady state diffusion. The effective diffusion coefficients were found to be of the order of 10^− 9 m² s^− 1 and were effected by the type of solute significantly. The WR, MC, WL and SG were predicted as weighted linear combinations of temperature, concentration of solute and time of OD.

Industrial relevance

The use of fructo-oligosaccharides (FOS) in different fruit based products is an efficient way to enrich human diet with functional component, because of the well-known health benefits of FOS. The osmotic behaviour of fructo-oligosaccharides were studied and compared to the conventional used sucrose. In view of the changes of different osmotics regarding to unit parameters of osmotic dehydration the results give possibility to industrial technology planning of products containing FOS, which are available for consumption in every season of the year and are favourable also in processed form e.g. muesli, dairy products.     

The use of various live animal measurements to predict carcass and meat quality in two divergent lamb breeds

Live weight, subjective scores of condition and conformation, live animal video image analysis (LVIA), ultrasound and X-ray computed tomography (CT) scanning were used to investigate the best method or combination of methods for predicting carcass and meat quality traits in live Texel and Scottish Blackface lambs. Predictors derived from CT alone accounted for a high proportion of the variance in dissected fat and muscle weight in Texel lambs (adjusted R² = 0.8), as well as intra-muscular fat content in the loin (0.6), but lower proportions in Blackface lambs (0.7 for fat, 0.4–0.5 for muscle and intra-muscular fat), after adjusting for sire and fixed effects. Adding traits measured by other in vivo methods increased prediction accuracies (adjusted R²) by up to 0.26, depending on trait and data set. Shear force and ultimate pH could not be accurately predicted using the traits considered here (adjusted R² < 0.4). Although the same methods tended to be best for predicting product quality traits between breeds, prediction accuracies differed.     

Effect of ionic strength and/or pH on Extractability and physico-functional characterization of broad bean (Vicia faba L.) Protein concentrate

Protein extractability studies showed that the protein of broad bean (Vicia faba L.) was extractable at both acidic and basic pH. The percentage of pH-12 extractable protein that was precipitated at pH 4 (isoelectric point) from protein concentrate, dehulled full-fat seed flour and whole seed flour are 62.0%, 61.2% and 71.6%, respectively. Low ionic strength (μ0.4) increased the solubility of the protein in the bean concentrate at acidic pH, while at alkaline pH, increase in ionic strength (0.1–2.0) had an inverse relationship on the concentrate protein solubility. The capacity to form protein-stabilized foam was least (34%) at pH 4 and highest (97%) at pH 12. These were increased to 62% (pH 4) and 139% (pH 12) in medium with ionic strengths of 0.2 and 0.4, respectively. The foam formed was more stable at pH 4 than at the other pHs. Low ionic strength of 0.1 improved water absorption capacity but reduced it at ionic strength of 0.6.     

On practical problems in estimation of antioxidant activity of compounds by DPPH method (Problems in estimation of antioxidant activity)

2,2′-Diphenyl-1-picrylhydrazyl (DPPH) method is commonly applied for the estimation of antioxidant activity of single compounds and their mixtures. The method is based on the spectrophotometric measurement of DPPH concentration changes resulting from the DPPH reaction with an antioxidant. The amount of remaining DPPH in the examined system is a measure of the antioxidative activity of compounds. The study shows that the type and amount of solvent used for the antioxidant dissolution, water content, and hydrogen or metal ion concentration in the measuring system significantly influence the differences in the amount of unreacted DPPH. The presence of ethyl acetate or dioxane or metal ions in the system decreases the kinetics of the reaction between DPPH and butylohydroxytoluene in relation to its kinetics in the system containing only methanolic solutions. The opposite effect is observed for water, low concentration of chloroform or hydrogen ions. The presented relationships confirm the necessity of standardising the DPPH method and show the complexity of the problem, even in very simple DPPH/antioxidant systems.     

Combined effect of an O2 absorber and oregano essential oil on shelf-life extension of Greek cod roe paste (tarama salad) stored at 4 °C

In the present study the combined effect of an O₂ absorber and oregano essential oil (0.1% v/w) on shelf life extension of Greek cod roe paste (tarama salad) stored under refrigeration (4 °C) was investigated. The study was based on microbiological [Total viable count (TVC), Lactic Acid Bacteria (LAB), Enterobacteriaceae, H₂S-producing, yeast and molds and Clostridium spp.), physicochemical (pH, fatty acid composition, thiobarbituric acid (TBA), and color) and sensory (color, odor, and taste) changes occurring in the product as a function of treatment and storage time. Aerobically packaged tarama salad stored at 4 °C was taken as the control sample. Results showed that TVC exceeded 7 log cfu/g on day 12–13 of storage for control samples and day 31–32 for samples containing oregano oil. Samples containing either the O₂ absorber or the O₂ absorber plus oregano oil never reached 7 log cfu/g during the 60 day storage period. LAB were only partially inhibited by the oregano oil and/or the O₂ absorber. Yeasts and molds were totally inhibited by the O₂ absorber. Enterobacteriaceae populations were below the method detection limit (2 log cfu/g) H₂S-producing bacteria were the dominant spoilage microorganisms. Clostridum spp. was absent in 25 g sample. pH decreased from an initial value of 4.36 to 3.03 depending on specific treatment. Color parameters L and b increased and a decreased in control samples as well as in samples containing oregano oil. Color parameters remained unaffected in samples containing the O₂ absorber. TBA expressed as malondialdehyde (MDA) values increased from 1.5 mg/kg to 3.4, 3.2 and 2.9 mg/kg for samples containing oregano oil, the O₂ absorber and O₂ absorber plus oregano oil at the point of sensory rejection, respectively. Saturated fatty acids (SFA) increased during storage with a respective decrease in monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) both in control samples and samples containing oregano oil. Fatty acid composition remained unaffected in all samples containing the O₂ absorber. Sensory shelf life was 24 days for the control samples, 32 days for samples containing oregano oil, 60 days for samples containing the O₂ absorber and at least 60 days for samples containing the O₂ absorber plus oregano oil.

Industrial relevance

Oxygen absorbers as well as plant essential oils are considered natural means of preservation and may substantially extend the shelf life of foodstuffs while maintaining desirable sensory attributes (taste, odor and color).     

Physicochemical properties of whey protein isolate stabilized oil-in-water emulsions when mixed with flaxseed gum at neutral pH

Concentrations ranging from 0% to 0.33% (w/v) of gum (Emerson and McDuff) were added to the emulsions at pH 7. Particle size distribution, viscosity, ζ-potential, microstructure, and phase separation kinetics of the emulsions were observed. Both polysaccharides and protein coated droplets are negatively charged at this pH, as shown by ζ-potential measurements. At all the concentrations tested, the addition of gum did not affect significantly (p < 0.05) the apparent diameter of the emulsion droplets. At low concentrations (gum  0.075% (w/v)), no visual phase separation was observed and the emulsion showed a Newtonian behaviour. However, at concentrations above the critical concentration of gum, depletion flocculation occurred: when 0.1 flaxseed gum was present, there was visual phase separation over time and the emulsion exhibited shear-thinning behaviour. These results demonstrate that flaxseed gum is a non-interacting polysaccharide at neutral pH; it could then be employed to strengthen the nutritional value of some milk-based drinks, but at limited concentrations.     

Total phenolic contents and antioxidant properties of commonly consumed vegetables grown in Colorado

A total of 38 commonly consumed vegetable samples, including 3 kale, 1 rhubarb, 3 spinach, 3 broccoli, 2 green bean, 5 carrot, 10 tomato, and 11 potato samples, were investigated for their total phenolic contents (TPC) and antioxidant properties. The measured antioxidant properties included free radical scavenging activities against DPPH, superoxide anion radical (O₂⁻), ABTS⁺ and peroxyl radical, and Fe²⁺ chelating capacity. The tested vegetables differed in their antioxidant properties and TPC, although all vegetables had significant antioxidant activities and contained significant levels of phenolics. The TPC and the measured antioxidant properties were correlated to each other. The Fe⁺² chelating capacity and the scavenging capacities against ABTS⁺, DPPH and O₂⁻ were reported for these commonly consumed vegetables for the first time. Results from this study suggest that kale, spinach, broccoli, and rhubarb are the better dietary sources of natural antioxidant activities and phenolic compounds. Furthermore, kale, broccoli and spinach produced in Colorado may have greater antioxidant contents than those grown at other locations.     

Comparison between free radical scavenging capacity and oxidative stability of nut oils

Several works have measured free radical scavenging capacity of nut oils, since they may become a significant source of dietary fat. However, they have not considered kinetic parameters, what was the first aim of this work. Also, it was studied the possible relation between values of free radical scavenging capacity DPPH and oxidative stability (Rancimat method) in different nut (hazelnut, peanut, pistachio, walnut and almond) oils. The ranking of antioxidant capacity of nut oils, by both assays, was: pistachio > hazelnut > walnut > almond > peanut. A significant correlation was found between DPPH and Rancimat methods assays. Tocopherols appear to be the responsible compounds of this antioxidant capacity being neglictible the contribution of polyphenols. An interference effect of phospholipids, present in methanolic fraction of nut oils, was observed in the determination of polyphenols in nut oils by Folin and ortho-diphenols assays.     

Performance and fat quality of heavy pigs fed maize differing in linoleic acid content

Maize shows wide differences in linoleic acid due both to total lipid content and to fatty acid profile. Therefore, diets containing the same high maize percentage (up to 55%) can differ in linoleic acid content and lead to subcutaneous fats of differing suitability for raw ham curing. Two trials were performed on heavy pigs; in the first, 60 pigs (body weight 48.7 ± 5.1 kg) were fed three diets made using three maize batches differing in linoleic acid due to different total lipid content, in the second trial, 40 pigs (live weight 70.4 ± 3.4 kg) were fed two diets made using two maize batches differing in linoleic acid due to their fatty acid profile. Pigs were slaughtered at 170 kg of live weight. In both trials, the growth and slaughtering performance did not differ. In the first trial the three diets lead to a different content of linoleic acid both in subcutaneous (low linoleic vs medium linoleic vs high linoleic P  0.01) and intramuscular fat (low linoleic vs high linoleic P  0.05). In the second trial different linoleic acid content was observed for subcutaneous fat (P  0.01) but not for intramuscular fat. To formulate diets for heavy pigs, it is crucial to know the linoleic acid content of the maize used, because differences of only 0.3% can lead to significant differences in fatty acids composition of depot fats.