Physical properties of whey protein coating solutions and films containing antioxidants

ABSTRACT:  Antioxidants (ascorbyl palmitate and α-tocopherol) were incorporated into 10% (w/w) whey protein isolate (WPI) coating solution containing 6.67% (w/w) glycerol (WPI:glycerol = 6:4). Before incorporation, the antioxidants were mixed using either powder blending (Process 1) or ethanol solvent-mixing (Process 2). After the antioxidant mixtures were incorporated into heat-denatured WPI solution, viscosity and turbidity of the WPI solutions were determined. The WPI solutions were dried on a flat surface to produce WPI films. The WPI films were examined to determine transparency and oxygen-barrier properties (permeability, diffusivity, and solubility). WPI solution containing antioxidants produced by Process 1 and Process 2 did not show any difference in viscosity and turbidity, but viscosity was greater for the WPI solution with rather than without antioxidants. WPI films produced by Process 2 were more transparent than the films produced by Process 1. Oxygen permeability of Process 1 film was lower than Process 2 film. However, both the diffusivity and solubility of oxygen were statistically the same in Process 1 and Process 2 films. Both control WPI films and antioxidant-containing WPI films had very low oxygen solubility, comparable to polyethylene terephthalate films. Permeability of antioxidant-incorporated films was not enhanced compared to control WPI films.     

Ultrasonication and Edible Coating Effects on Lipid Oxidation of Roasted Peanuts

Lipid oxidation is an important factor affecting the quality of roasted peanuts. Coatings applied to the peanuts can enhance oxygen barriers to reduce rancidity. Ultrasonication was used to remove lipids from the peanuts prior to applying the coating to improve attachment of the coating on the peanut surface. Peanuts were roasted at 178°C for 15 min and then sonicated in hexane for 10 min. Whey protein isolate (WPI) 11%, corn protein (Zein) 15%, and carboxymethyl cellulose (CMC) 0.5% were used as coating materials. Sample treatments were: (1) roasted–coated with CMC (RCMC), WPI (RWPI), and Zein (RZEIN); (2) roasted–sonicated–coated with CMC (SCMC), WPI (SWPI), and Zein (SZEIN); (3) roasted–uncoated (R) as a control. Oxidative stability was investigated by gas chromatography–mass spectrometry (GC–MS) to detect formation of volatile compounds. The GC–MS indicated an eightfold, fivefold, and fourfold increase in hexanal formation in R, RZEIN, and SZEIN samples, respectively. But there was 80%, 91%, 18%, and 66% decrease in hexanal formation in RCMC, SCMC, RWPI, and SWPI samples, respectively, as compared to R. Sonication increased capability of coatings to delay hexanal formation by 11% and 48% for CMC and WPI, respectively, as compared to nonsonicated samples. Thus, the coating in combination with ultrasonication treatment was an effective method in delaying formation of oxidative volatile compounds and hence inhibiting rancidity of roasted peanuts.     

The effectiveness of butylated hydroxyanisole and α‐tocopherol in inhibiting oxidant‐induced chemical and structural changes of whey protein

The objective of the study was to investigate the role of butylated hydroxyanisole (BHA) and α‐tocopherol in protecting whey protein isolate (WPI) from oxidative modification. The results showed that oxidation increased protein carbonyls and decreased total sulfhydryls, and led to higher dityrosine and surface hydrophobicity (P < 0.05) than nonoxidised WPI. The presence of BHA and α‐tocopherol significantly reduced (P < 0.05) the extent of WPI oxidation, thus limiting the oxidation‐induced protein aggregates and structural changes. Therefore, BHA and α‐tocopherol may be used as potential antioxidants in WPI and WPI‐containing foods.     

Listeria monocytogenes Inhibition by Whey Protein Films and Coatings Incorporating the Lactoperoxidase System

Antimicrobial effects of whey protein isolate (WPI) films and coatings incorporating the lactoperoxidase system (LPOS) against Listeria monocytogenes were studied by turbidity, plate counting, disc‐covering, and disc‐surface‐spreading tests using various growth media. Survival of L. monocytogenes applied to smoked salmon before or after the coating was monitored immediately after application and during storage at 4 °C and 10 °C for up to 35 d. Tensile properties (elastic modulus [EM], tensile strength [TS], elongation [E]), oxygen permeability (OP), and color (Hunter L, a, b) of WPI films, with and without LPOS, were also compared. LPOS inhibited L. monocytogenes in broth and on agar media. WPI films incorporating 29 mg of LPOS per gram of film (dry basis) inhibited 4.2 log colony‐forming units (CFU)/cm² of L. monocytogenes inoculated on agar media. WPI coatings prepared with LPOS at 0.7% (w/w) in a coating solution (40 mg LPOS/g coating [dry basis]) initially reduced >3 and 1 log CFU/g of L. monocytogenes and total aerobic microorganisms in smoked salmon, respectively. The WPI coatings incorporating LPOS prevented the growth of L. monocytogenes in smoked salmon at 4 °C and 10 °C for 35 d and 14 d, respectively. The tensile properties, oxygen permeability, and color of WPI films were not significantly changed by incorporation of LPOS (P >0.05).     

IMPROVEMENT OF OXIDATIVE STABILITY OF ROASTED PEANUTS BY EDIBLE COATINGS AND ULTRASONICATION

In this study, an innovative method was developed to improve the shelf life of roasted peanuts. Sonication was combined with edible coating for enhancing the oxidative stability of roasted peanuts. Georgia green runner peanuts were roasted, subjected to sonication and then coated with whey protein isolate (WPI), ZEIN and carboxymethyl cellulose (CMC). Relative to the control, the oxidative stability of roasted-coated samples was improved by 80, 38 and 5% for CMC, WPI and ZEIN coating, respectively, while roasted-sonicated-coated samples were improved by 91, 52 and 27% for CMC, WPI and ZEIN coating, respectively. Sonication prior to coating resulted in 11, 14 and 22% improvement beyond the CMC, WPI and ZEIN coatings, respectively. Texture analysis showed there were no significant differences ( P <  0.05) in peanut texture between the treated and the control. Color results showed the HunterLab color parameters L, a, and b for most of the treatments did not have significant differences ( P <  0.05) compared with the control.

PRACTICAL APPLICATIONS

Edible coatings used in this study (carboxymethyl cellulose, whey protein isolate and ZEIN) were capable of acting as oxygen barriers to reduce peanut lipid rancidity. This research demonstrated the potential of power ultrasound to remove lipids from the peanut surfaces and improve coating adhesion. The texture and the color of coated peanuts did not change over the storage period. This study indicated that edible coatings in combination with sonication provided an alternative way for improving the oxidative stability and eventually the shelf life and quality of roasted peanuts.     

Whey Protein Coating Effect on The Oxygen Uptake of Dry Roasted Peanuts

A procedure was developed to coat peanuts with aqueous whey protein isolate (WPI) solutions based on increasing coating-solution viscosity. Oxygen uptake of WPI-coated nuts and uncoated nuts were compared. WPI coatings delayed oxygen uptake of dry roasted peanuts at intermediate (53%) and low (21%) storage relative humidity. They had similar results at 29°C and 37°C. The effects of coating thickness and storage relative humidity indicate that the mechanism of protection of the coatings was through their oxygen barrier properties.     

Edible Coatings on Frozen King Salmon: Effect of Whey Protein Isolate and Acetylated Monoglycerides on Moisture Loss and Lipid Oxidation

Whey protein isolate (WPI) and acetylated monoglyceride (AMG) coatings were evaluated for effectiveness against moisture loss and lipid oxidation of frozen King salmon. A model gel material was also used to screen coatings for effectiveness against moisture loss. Coatings of low-melting-point AMG used alone or after applying WPI solution or WPI powder were effective in reducing the rate of moisture loss by 42–65% during the first 3 wk of storage. Onset of lipid oxidation was delayed and peak peroxide values were reduced in samples coated with WPI solution/antioxidant overspray or those containing low-melting-point AMGs. No differences in effectiveness were found among the coating treatments.     

Whey Protein-Sucrose Coating Gloss and Integrity Stabilization by Crystallization Inhibitors

ABSTRACT: Whey protein coatings protect foods from change and deterioration and can extend product shelf life. However, because they are also made from food materials, whey protein coatings may also change over time if not properly formulated. Whey protein isolate (WPI)-sucrose high-gloss coatings, with and without crystallization inhibitors, were formed on chocolate-covered peanuts. The objective was to determine the effectiveness of crystallization inhibitors on preventing cracking of coatings and loss of coating gloss caused by sucrose crystallization during product storage. The 4 inhibitors tested were lactose, modified starch, polyvinylpyrrolidone, and raffinose. The WPI-coated chocolate-covered peanuts were stored for 119 d in 23%, 33%, and 44% relative humidity (RH) at 25°C. Gloss of the WPI coatings was measured periodically with a gloss-analysis system. It was found that raffinose is the most effective inhibitor of sucrose crystallization in whey protein-sucrose coatings. WPI coatings containing raffinose had significantly higher gloss values than all other coatings. For raffinose-containing samples stored in 23% and 33% RH environments, less than 3% of gloss was lost during storage. In 44% RH, the raffinose coating system had significantly less gloss fade than other WPI-sucrose coatings. This information can be used to improve the effectiveness of water-based high-gloss edible coatings.     

Preserving sensory attributes of roasted peanuts using edible coatings

Peanut products are susceptible to develop rancid and off‐flavours through lipid oxidation. Preservation of these products is one of the problems in the peanut industry. The purpose of this work was to determine the sensory and chemical stability of roasted peanuts (RP) coated with different edible coatings: carboxymethyl cellulose (RP‐CMC), methyl cellulose (RP‐MC) or whey protein (RP‐WPI) during storage. Sensory attributes and chemical indicators (peroxide and p‐anisidine values, and conjugated dienes) of lipid oxidation were measured during storage. Chemical indicator values and intensity ratings of oxidised and cardboard flavours had lower increase in RP‐CMC, RP‐MC and RP‐WPI during storage than in RP, whereas roasted peanutty flavour showed a lower decrease. The stability of RP‐CMC is about a double longer with respect to RP. These results indicate that edible coatings preserve the sensory properties of roasted peanuts. Carboxymethyl cellulose exhibited the best protecting effect on this product.     

Influence of Whey Protein Composite Coatings on Plum (Prunus Domestica L.) Fruit Quality

This study evaluated the quality of plums (Prunus domestica L.) coated with whey protein isolate (WPI) and WPI composite coatings containing 5 or 10% (w/w) flaxseed oil blended with beeswax. WPI and 10% lipid composite coatings were less susceptible to crack, flake, and blister defects during the 15 days storage at 5°C compared to the 5% lipid formulation. The firmness of plums, determined by the penetration force using a 10-mm probe, was not significantly affected by the coating types except for the WPI-coated samples, which showed a significantly higher penetration force because of the higher strength for WPI film. Mass loss of plums during storage was substantially reduced because of coating, especially when coatings of higher lipid content were used. This was consistent with the water permeability for the standalone films, which decreased considerably when flaxseed and beeswax were added. The incorporation of lipid phase to WPI also significantly weakened oxygen barrier and mechanical properties. Migration of plasticizer and lipid phase to the film surface was observed during water vapor permeability tests, especially when the films were exposed to elevated humidity conditions. Overall, sensory evaluation showed that the coated plums were more acceptable than the uncoated controls.     

Rehydration characteristics of freeze‐dried strawberry pieces as affected by whey protein edible coatings

This paper is about the use of whey protein isolate (WPI) edible coatings to improve the rehydration behaviour of freeze‐dried (FD) strawberry pieces. First, the optimal ratio sample mass/volume of coating solution was optimised by determining the rehydration ratio, bulk density and nutritional quality of the samples. Coating time is also determined in coated samples by light microscopy. Second, the effect of changing the pH and the variation in temperature–time to denaturate WPI on rehydration characteristics was also evaluated. The rehydration ratio of strawberry pieces decreased with increasing the denaturation temperature and denaturation time, while it increased with increasing pH of the coating solution. Third, according to the rehydration curves, coating was not a single layer but small pieces attached to strawberry pieces. The soluble protein contents in water after rehydration confirm this conclusion.     

Oxidative Stability of Anhydrous Milkfat Microencapsulated in Whey Proteins

The chemical stability was studied on anhydrous milkfat (AMF) encapsulated in whey protein isolate (WPI) and WPI combined with lactose (1:1 w/w WPI/L). AMF-containing microcapsules, as well as bulk milkfat, were stored at 20°C with light, 40°C without light, and 50°C with and without light for up to 12 mo. Milkfat oxidation was monitored by oxygen uptake in headspace and hexanal accumulation. In all cases, AMF oxidation was significantly limited by microencapsulation in WPI or WPI/L. Whey proteins are effective microencapsulating agents.     

Antioxidant ability of BHT‐ and α‐tocopherol‐impregnated LDPE film in packaging of oatmeal

Cereals in general, and particularly oatmeals, are considered rather sensitive to oxidation owing to their relatively high fat content. The addition of antioxidants can sometimes prolong the shelf‐life of products. The aim of the present study was to investigate how the rate of lipid oxidation of a packaged oatmeal product was affected by the nature and level of antioxidants incorporated in an LDPE film structure. The stability of the product, which was determined by hexanal analysis using GC–MS and by electronic nose analysis, showed very small variations over the chosen storage period. No oxidation, as determined by hexanal levels in the oatmeal, was initiated during storage, but small variations in volatile profile were seen among the samples analysed by the electronic nose. The product stored in the BHT‐impregnated LDPE film had undergone the least change during 10 weeks of storage at 20 °C. α‐Tocopherol‐impregnated LDPE film did not appear to prolong the shelf‐life of the oatmeal at all. © 2000 Society of Chemical Industry     

FLUIDIZED-BED SYSTEM FOR WHEY PROTEIN FILM COATING OF PEANUTS

Complete peanut‐surface coverage and strong adhesion are necessary for whey protein‐based oxygen barrier coatings to be totally effective in reducing the oxidative rancidity of peanuts. Peanuts coated with a fluidized‐bed coating system attained practically complete coverage, and coating efficiency results were consistent and reproducible. Addition of surfactant to the coating solution improved whey protein coating efficiency on blanched/roasted peanuts coated with a bench‐scale fluidized‐bed coating system. A lower level of surfactant addition to the coating solution was required to attain complete coverage, compared with previous studies on dip coating and pan coating of peanuts. Addition of surfactant to the coating solution and peanut preroughening both imparted good coating adhesion for fluidized‐bed‐coated peanuts. Compared with pan coating, fluidized‐bed coating required application of a greater amount of coating solution because of the loss of coating solution to the fluidized‐bed column wall during spraying. Overall, fluidized‐bed coating required a shorter processing time and provided the peanuts with better coating efficiency and adhesion. These results suggest that a fluidized‐bed coating system is a viable alternative coating process for whey protein coating of peanuts.     

Protein-based coatings on peanut to minimise oil migration

Soy protein isolate (SPI) or calcium caseinate (CC)-based coatings were applied on peanuts as a barrier of oil migration, and their efficiency was evaluated. These coatings induced a decrease of oil migration as compared to the uncoated peanuts. Subsequently, three polysaccharides were individually added to the coating solution to prevent oil migration further. The incorporation of carboxymethylcellulose (CMC) with SPI and CC coating solutions significantly (p ? 0.05) decreased the migration of oil as compared to the coatings without CMC. The addition of pectin seemed unfavourable because it enhanced the migration of oil. Starch in SPI-based coating solution helped to decrease the oil migration, but it did not affect the migration level in samples treated with CC solution. The results from size-exclusion chromatography showed strong cross-links by glutaraldehyde and transglutaminase treatments in SPI and CC-based coating solutions. A strong cross-linking in protein-based coating correlated closely with a reduction in oil migration. For both proteins, the cross-linking by transglutaminase was most efficient for improving the effectiveness of coating. This study demonstrated that our protein-based coatings can be effectively implemented to food industry for better quality of peanut products.     

抗氧化剂对羟自由基引起的乳清分离蛋白氧化抑制效果的研究

采用羟自由基对乳清分离蛋白(WPI)进行氧化,并采用在氧化前添加抗氧化剂的方法,研究其对乳清分离蛋白氧化的抑制作用。实验分为3 组,即不添加抗氧化剂的对照组、添加α- 生育酚和丁羟基茴香醚(BHA)的处理组,测定氧化1、5h 和12h 后WPI 羰基、总巯基、二聚酪氨酸、表面疏水性和SDS-PAGE 的变化。结果表明,蛋白氧化会显著提高WPI 中的羰基含量和二聚酪氨酸含量(P ＜ 0.05),而且会使蛋白质的疏水性增加(P ＜ 0.05)。添加α- 生育酚和BHA 的乳清蛋白氧化5h,与对照组相比可以使羰基含量降低 35.11% 和50.15%,巯基含量增加27.73% 和38.82%。通过SDS-PAGE 表明,添加抗氧化剂可以减少蛋白质的聚合。抗氧化剂的添加抑制了乳清蛋白的氧化。     

Moisture Loss and Lipid Oxidation for Precooked Ground-Beef Patties Packaged in Edible Starch-Alginate-Based Composite Films

Edible films of starch‐alginate (SA), starch‐alginate‐stearic acid (SAS), SA‐tocopherol, SAS‐tocopherol, tocopherol‐coated SA film, and tocopherol‐coated SAS film were evaluated for their effectiveness in maintaining quality of precooked beef patties stored at 4 °C. Patty weight loss, moisture loss, 2‐thiobarbituric acid‐reactive substances value, the formation of hexanal, pentane, and total volatiles of samples differed with film composition. SAS‐based films were more effective (P < 0.05) in controlling moisture loss than lipid oxidation. Tocopherol‐treated films were more effective (P < 0.05) in inhibiting lipid oxidation than were nontocopherol films. Most of the tested edible films were not as effective as polyester vacuum bags in retarding moisture loss and lipid oxidation.     

Flavonoids quercetin,myricetin, kaemferol and (+)‐catechin as antioxidants in methyl linoleate

The antioxidant effect of the flavonoids quercetin, myricetin, kaemferol, (+)‐catechin and rutin on methyl linoleate oxidation was investigated. In addition, the synergistic effects of flavonoids and α‐tocopherol were studied. Oxidation was monitored by conjugated diene measurement and by determining the formation of hydroperoxide isomers by HPLC. The antioxidant activity of flavonoids in non‐polar methyl linoleate differ from that previously reported in water‐containing systems, such as LDL and liposome systems. The activity of antioxidants (10–1000 μM ) measured by hydroperoxide formation decreased in the order: myricetin>quercetin>α‐tocopherol>(+)‐catechin >kaemferol=rutin. The antioxidant activity of flavonoids increased as the number of phenolic hydroxyl groups increased. In addition to the number of hydroxyl groups, other structural features such as the 2,3 double bond in the C‐ring and a glycoside moiety in the molecule had an effect on the antioxidant activity. Myricetin and rutin, especially had a synergistic effect with α‐tocopherol. Myricetin, quercetin and rutin protected α‐tocopherol from decomposition, myricetin being the most protective. The relative hydrogen‐donating activity measured by the ratio of cis,trans‐ to trans,transhydroperoxide isomers formed during oxidation decreased in the order: α‐tocopherol >myricetin>quercetin. Hydroperoxide isomeric distribution of the samples containing kaemferol or rutin did not differ from the control. Thus, although α‐tocopherol was the most effective hydrogendonor, myricetin and quercetin were more effective antioxidants in inhibiting the hydroperoxide formation in methyl linoleate. © 1999 Society of Chemical Industry     

Influence of sn‐1,3‐lipase‐catalysed interesterification on the oxidative stability of soybean oil‐based structured lipids

The oxidative stability of structured lipids (SLs) synthesised by specific sn‐1,3‐lipase catalysed interesterification of soybean oil (SBO) with caprylic acid (CA) in a stirred batch reactor was studied. SLs contained considerable amounts of tocopherol (TOH) isomers, although they lost almost 25% of endogenous TOHs during production. The effects of the addition of different TOH homologues (α, β, γ, δ), ascorbyl palmitate (AP, 200 ppm), lecithin (Le, 1000 ppm), butylated hydroxytoluene (BHT, 100 ppm) and butylated hydroxyanisole (BHA, 100 ppm) on the oxidative stability of SLs were investigated. Induction time (IT) of SBO, determined by the Rancimat method, decreased from 8.4 to 5.8 h at 110 °C after the modification. On the other hand, purified SLs and purified SBO had the same IT due to the tocopherol reduction during silica purification. No significant difference was observed between IT of SLs and SLs plus different α‐tocopherol concentrations (50, 100, 150, 200, 300, 500 and 1000 ppm) (P > 0.05). However, the addition of Le and/or AP significantly improved oxidative stability of purified SLs and SBO. The ternary blend containing δ‐TOH, AP and Le had higher IT than ternary blends of α‐TOH, β‐TOH or γ‐TOH. Furthermore, ternary blend containing BHA, AP and Le had higher IT than ternary blends of BHT, AP and Le. In addition, there was an increase in peroxide value (PV), conjugated diene (CD) content and p‐anisidine value (AV) during oxidation of oils at 60 °C. Antioxidant mixtures of α‐TOH (50 ppm) and δ‐TOH (500 ppm) with AP and Le decreased PV, CD and AV effectively. Copyright © 2006 Society of Chemical Industry     

Antioxidant activity and characterization of volatile constituents of beechwood creosote

Volatile constituents of beechwood creosote were determined using gas chromatography (GC) and gas chromatography–mass spectrometry (GC‐MS). The major volatile constituents of creosote were 2‐methoxyphenol (guaiacol; 25.2%) 2‐methoxy‐4‐methylphenol (4‐methylguaiacol; 21.4%), 3‐methylphenol (m‐cresol; 8.3%) 4‐methylphenol (p‐cresol; 7.9%) 2‐methylphenol (o‐cresol; 4.6%) and phenol (2.8%). The antioxidant activity of creosote was evaluated by three different chemical assays. Beechwood creosote exhibited potent inhibitory effects on the formation of conjugated diene hydroperoxides (from methyl linoleate) at concentrations of 500, 750 and 1000 µg ml^?1. Creosote had a potent inhibitory effect on the oxidation of hexanal for 40 days at a level of 5 µg ml^?1 and also inhibited malonaldehyde (MA) formation from ethyl arachidonate by 92% at a level of 50 µg ml^?1. The antioxidative activity of creosote was comparable with that of the well‐known antioxidants α‐tocopherol and BHT in the hexanal assay. However, creosote displayed comparatively lower antioxidant activity in the other two assays. Copyright © 2005 Society of Chemical Industry