Enzymatic and Autoxidation of Defatted Peanuts

Ground, blanched, raw, and roasted peanuts with varying oil contents were analyzed for oxidation products. Peroxide values (PV) of blanched, ground raw (BRAW) peanuts, demonstrating enzymatic oxidation, and heat-treated rancid roasted peanuts (RRST), demonstrating autoxidation, exhibited decreases (p ≦ 0.05) with decreasing oil content. The Oxidative Stability Index (OSI) time at 110 °C increased (p < 0.05) with decrease in oil content of raw (BRAW) and roasted (BRST) ground peanuts. A higher OSI indicated more oxidative stability, thereby supporting the hypothesis of higher potential for autoxidation at higher oil contents. In addition, BRST exhibited a shorter OSI than BRAW, indicating slower autoxidation in BRAW. Roasted peanutty odor, burnt odor, and roasted peanutty flavor, rancid/oxidized flavor, and burnt flavor scores of rancid roasted peanuts decreased (p ≦ 0.05) with decreasing oil content.     

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.     

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.     

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.     

Mycoflora and Aflatoxin Content of Hazelnuts,Walnuts, Peanuts,Almonds and Roasted Chickpeas (LEBLEBI) Sold in Turkey

In this study, 28 hazelnuts, 24 walnuts, 18 peanuts, 13 almonds, and 11 roasted chickpeas (leblebi) were analyzed for aflatoxin contamination using thin layer chromatography (TLC). Aflatoxin was found in 26 of 94 samples (27.66%) at concentrations ranging from 1 to 113 ppb. Detectable levels of aflatoxin were 33.4 ppb in hazelnuts, 22.1 ppb in walnuts, 43.0 ppb in peanuts, 7.4 ppb in almonds, and 1.7 ppb in roasted chickpeas. The highest level of aflatoxin was 113 ppb in a single hazelnut sample. Aspergillus and Penicillium species were frequently determined in all the samples.     

Effects of Hot Air-assisted Radio Frequency Heating on Quality and Shelf-life of Roasted Peanuts

Roasting is a critical step in processing peanut snack foods. The conventional roasting using hot air ovens has drawbacks of low production rate, poor product quality, and high energy cost. This study investigated the feasibility of using hot air-assisted radio frequency (RF) to roast dried salted peanuts. Physicochemical properties, volatile compounds, and sensory quality of the roasted peanuts were determined. The quality changes and shelf-life of vacuum-packaged roast peanuts stored under an accelerated shelf-life testing (ASLT) trial conducted at 20 and 50 °C were also evaluated. After 45 min roasting, moisture content of the salted peanuts reduced from initial 7.7 to 3.1 % and acid and peroxide values were 0.26?±?0.02 mg/g and 2.46?±?0.10 meq/kg, respectively, all in the levels associating with good quality of roasted peanuts. Sensory evaluation further validated the good quality of the roasted peanuts. Totally, 69 volatile compounds were identified in the roasted peanuts, in which 3 new volatiles were produced after about 13 weeks of storage. During the storage, relative concentrations of the favorable volatile compounds (mainly pyrazines and furan compounds) decreased in a certain degree, while the relative concentrations of some undesirable flavor compounds increased. The roasted peanuts had 31 weeks of shelf-life based on the industrial standard on the peroxide value. This study demonstrated that hot air-assisted RF roasting can produce high-quality roasted peanuts with prolonged shelf-life, thus, a new technology for the peanut roasting industry.     

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.     

核桃仁氧化酸败及其延缓措施研究进展

核桃是世界四大干果之一,果仁营养丰富,经济价值颇高。但由于核桃仁脂肪含量高,贮藏中易出现脂肪氧化酸败现象。对核桃仁氧化酸败的机理及影响酸败的温度、相对湿度、氧气、光照、含水量等因素进行探讨。同时,综述延缓核桃仁氧化酸败的相应措施,以期为核桃仁的大规模贮藏提供理论参考。     

Tocopherol content,peroxide value and sensory attributes in roasted peanuts during storage

The objective of this study was to determine changes in tocopherol content, peroxide value (PV) and sensory attributes from roasted peanuts during storage at 40 °C. There were no differences in tocopherol contents between roasted and raw peanuts except in α‐tocopherol content that decreased after roasting. All tocopherol contents decreased during storage. On the contrary, lipid oxidation indicators such as PV and the intensity ratings of oxidised and cardboard flavour increased during storage. On the other hand, the intensity ratings of roasted peanutty flavour decreased with storage time. Good correlations were observed between tocopherol contents and PVs. Tocopherol contents could be used as indicator of oxidative state in peanut products.     

Vitamin E and Oxidative Stability During Storage of Raw and Dry Roasted Peanuts Packaged under Air and Vacuum

ABSTRACT: The relationship between vitamin E and the oxidative stability of raw and dry roasted peanuts was studied during storage at 21°C under air and vacuum. Lipid oxidation was monitored by peroxide values (PVs) and conjugated diene values (CDVs). In air, PV (meq/kg) for roasted peanuts reached 47 by 12 wk, whereas that for raw peanuts was below 2 after 38 wk. Under vacuum, lipid oxidation was significantly retarded ( P < 0.05). Tocopherols of raw and roasted peanuts exponentially decreased with increasing PV. After 12 wk, about 50% of α-tocopherol (α-T) was lost for roasted peanuts under vacuum compared with about 90% under air. For raw peanuts, more than 70% of each tocopherol remained after 38 wk under air and vacuum. In general, α-T showed the least stability in roasted peanuts compared with other tocopherols under the reported storage conditions.     

Influence of Tertiary Butylhydroquinone and Certain Other Surface Coatings on the Formation of Carbonyl Compounds in Granulated Roasted Peanuts

A 15-month shelf life study was conducted with granulated roasted peanuts (Arachis hypogaeu L.). The nuts were coated with combinations of 0.01, 0.02, and 0.03% tertiary butylhydroquinone (TBHQ) antioxidant, two fats and an acetylated monoglyceride. Total carbonyls were measured monthly and served as an index of oxidative rancidity. TBHQ combined with citric acid was an effective anitoxidant in inhibiting carbonyl production, while the fats and monoglyceride coatings alone had no significant effect on carbonyl production. Samples without TBHQ exhibited a fivefold increase in total carbonyl content compared with samples treated with TBHQ. Total carbonyl levels of granulated peanuts treated with 0.02% TBHQ, the level presently allowed by the FDA, increased 20% during the 15-month storage period compared with an increase of 110% for those without TBHQ.     

Effects of processing conditions and packaging material on the quality attributes of dry‐roasted peanuts

Five different processing conditions of raw shelled unblanched peanuts were investigated. The first two treatments involved soaking the peanuts in tap water for 10 and 30 min respectively, then mixing thoroughly with dry NaCl before roasting. Another two treatments involved soaking the peanuts in saturated brine solution for 10 and 30 min respectively before roasting. Unsalted roasted peanuts served as the control. Packaging and storage studies were carried out by packaging the differently treated dry‐roasted peanuts in four different packaging materials and storing them under three different relative humidities for 3 months at ambient temperature. Proximate composition, NaCl content, peroxide value and thiobarbituric acid value were determined and sensory evaluation tests were carried out. Salting was found to improve the taste, flavour and overall acceptability of dry‐roasted peanuts but had no effect on shelf‐life. Peanuts treated in saturated brine solution for 30 min before roasting were the most preferred. The control packaging material, 18 µm transparent polyethylene, was found to be inadequate for protecting the quality attributes of dry‐roasted peanuts, with mould growth being observed on the 42nd day of storage at 80% relative humidity. However, acceptable results were obtained with 45 µm transparent polypropylene. The mean sensory scores and objective tests were found to be negatively correlated. © 2002 Society of Chemical Industry     

Characterization of edible coatings consisting of pea starch, whey protein isolate, and Carnauba wax and their effects on oil rancidity and sensory properties of walnuts and pine nuts

Edible coatings made of whey protein isolate (WPI), pea starch (PS), and their combinations with carnauba wax (CW) were prepared and characterized. WPI combined with CW formed stable emulsion while PS with CW formed unstable emulsion and both formulations produced non-homogeneous films. Addition of PS to WPI: CW combination at the ratio of 1:1:1, respectively, resulted in stable emulsion and homogenous films. The emulsion PS: WPI: CW (1:1:2) was stable and formed a continuous film but had less homogenous droplets size distribution when compared to 1:1:1 film. Combined films had a reduced tensile strength and elongation compared to single component films. WPI : CW (1:1) films had higher elastic modulus than the WPI films, but the modulus reduced by the addition of PS. All the coating formulations were effective in preventing oxidative and hydrolytic rancidity of walnuts and pine nuts stored at 25 °C throughout the storage (12 d) but were less effective at 50 °C. Increasing the concentration of CW from 1:1:1 to 1:1:2 in PS: WPI: CW formulation did not contribute in further prevention of oil rancidity at 25 °C. Using of PS: WPI: CW (1:1:1) coating on both nuts significantly (P < 0.05) improved their smoothness and taste but the PS: WPI: CW (1:1:2) coatings imparted unacceptable yellowish color on walnuts. PRACTICAL APPLICATION: Edible coating of walnuts and pine nuts by whey protein isolate, pea starch, and carnauba wax reduced the oxidative and hydrolytic rancidity of the nuts and improved sensory characteristics.     

Chemometric evaluation of trace metal concentrations in some nuts and seeds

Seventeen trace metals in acid digests of nuts and seeds were determined using inductively coupled plasma-atomic emission spectrometry and inductively coupled plasma-mass spectrometry. The data were subjected to chemometric evaluation using principal component analysis (PCA), linear discriminant analysis (LDA) and cluster analysis (CA) in an attempt to classify the samples. Hazelnuts (raw and dry roasted), almonds (raw and dry roasted), sunflower seeds (black and white), peanuts (raw and dry roasted), cashew nuts, Brazil nuts, walnuts, chickpeas (raw and dry roasted), pumpkin seeds (raw and dry roasted), and pistachio nuts were used as samples. The samples were classified into seven groups by PCA and CA. All group members determined using PCA and CA were found by LDA to be correctly classified in the predicted groups. Interestingly, the chemometric evaluation indicated that the raw and roasted nuts are very close to each other even though some originated from different countries.     

Lipoxygenase activity in walnuts and almonds

The objective of this experiment was to investigate lipoxygenase (LOX) activity in walnut or almond homogenates. Walnut or almond kernels were heated with hot air at 55 °C for 2 or 10 min, or 60 °C for 2 or 10 min. The homogenates of untreated or heat treated walnut kernels exhibited greater LOX activity than the homogenates of untreated or heat treated almond kernels. Short-time heat treatments of 55 °C for 2 min or greater reduce LOX activity, retard the development of oxidative rancidity, and extend the shelf-life of walnuts and almonds during distribution and storage. Short-time heat treatments of walnut or almond kernels designed to control insect pests for international trade did not promote rancidity when compared to untreated walnuts or almonds.     

The development of rancidity in husked and naked oats after storage under various conditions

The levels of hydrolytic and oxidative rancidity have been estimated in husked and naked (huskless) oat varieties stored under different conditions, viz. (i) varying moisture content, (ii) varying oxygen availability, (iii) after bruising, and (iv) after drying at different temperatures. Hydrolytic rancidity increased at higher moisture contents and with storage period but generally the level in naked oats only exceeded that of husked oats if the grain was severely bruised. No oxidative rancidity was detected in husked or naked oats under any of the treatments used.     

Polyphenolic and antioxidant changes during storage of normal,mid, and high oleic acid peanuts

The quality of dry roasted peanuts is highly dependent on storage conditions for preventing oxidation of fatty acids; however, changes in polyphenolics affecting antioxidant capacity due to co-oxidative reactions are unknown. The objective of this work was to evaluate oxidative stability of polyphenolics in peanut kernels with naturally varying rates of lipid oxidation. Three peanut varieties containing varying levels of oleic acid (normal, mid, and high) were dry roasted and evaluated for phytochemical changes over four months of storage at 20 and 35 °C; analyses included peroxide value, total and individual phenolics and antioxidant capacity. The normal oleic acid peanuts suffered up to 2.6-fold and mid-oleic acid peanuts 2-fold more lipid oxidation than the high-oleic acid peanuts stored at 35 °C. Changes in total soluble phenolics were initially similar among cultivars, but antioxidant capacity was found to decrease by 62%, on average, during storage at 35 °C, independently of rates of lipid oxidation. Free p-coumaric acid, three esterified derivatives of p-coumaric, and two esterified derivatives of hydroxybenzoic acid were the predominant polyphenolics present and their rates of change were similar among cultivars and independent of storage time or temperature. The high-oleic acid content was essential for prevention of lipid oxidation, but data indicated that co-oxidative reactions, affecting polyphenolic content during storage, were not great enough to significantly alter antioxidant capacity.