Almond Skin Research Articles

Polyphenol content and antioxidant activity of California almonds depend on cultivar and harvest year

The polyphenol content and antioxidant activity of Nonpareil, Carmel, Butte, Sonora, Fritz, Mission, and Monterey almond cultivars harvested over three seasons in California were examined. LC–MS was employed to quantify 16 flavonoids and two phenolic acids in acidified methanol extracts of almond skins. The 3-year mean polyphenol content of cultivars ranged from 4.0 to 10.7 mg/100 g almonds. Isorhamnetin-3- O-rutinoside was the most abundant flavonoid, present at 28–49% of total polyphenols among cultivars. Almonds from 2006 and 2007 had 13% fewer polyphenols than 2005, but FRAP and total phenols were comparable. Cultivar, but not season, had a differential impact on individual polyphenol synthesis. Using the results of polyphenol, total phenol, and FRAP, multivariate analysis distinguished harvest years and most cultivars with 80% confidence. Flavonoid content and antioxidant activity of almonds may be more dependent on cultivar than on seasonal differences.

Cytoprotection by almond skin extracts or catechins of hepatocyte cytotoxicity induced by hydroperoxide (oxidative stress model) versus glyoxal or methylglyoxal (carbonylation model)

Oxidative and carbonyl stress are detrimental in the pathogenesis of diabetic complications, as well as in other chronic diseases. However, this process may be decreased by dietary bioactive compounds. Almond skin is an abundant source of bioactive compounds and antioxidants, including polyphenolic flavonoids, which may contribute to the decrease in oxidative and carbonyl stress. In this study, four Almond Skin Extracts (ASEI, ASEII, ASEIII, and ASEIV) were prepared by different methods and evaluated for their antioxidant activity. The order of the polyphenol content (total μM gallic acid equivalents) of the four extracts was found to be, in decreasing order of effectiveness: ASEI > ASEIII > ASEIV > ASEII. The order of Ferric-reducing antioxidant power (FRAP, μM FeSO 4/g) value, in decreasing order was ASEI (216) > ASEIII (176) > ASEIV (89) > ASEII (85). The order of ASE effectiveness for decreasing protein carbonyation induced by the copper Fenton reaction was ASEI > ASEIV > ASEII > ASEIII. The order of antioxidant effectiveness for inhibiting tertiary-butyl hydroperoxide (TBH) induced microsomal lipid peroxidation was ASEI > ASEIV > ASEII, ASEIII. Also, the order of ASE effectiveness for inhibiting TBH induced hepatocyte cell death was: ASEIII, ASEIV > ASEI, ASEII. Catechin also protected hepatocytes from TBH induced hepatocyte, lipid peroxidation and cytotoxicity. In a cell free model, equimolar concentrations of catechin or epicatechin rescued serum albumin from protein carbonylation induced by methylglyoxal (MGO). Catechin, epicatechin and ASEI all decreased gloxal induced hepatocyte cell death and reactive oxygen species (ROS) formation in GSH-depleted hepatocytes. Catechin and epicatechin protected against GO or MGO induced hepatocyte cell death, protein carbonylation and ROS formation. Catechin was more effective than epicatechin. Our results suggest that (a) bioactive almond skin constituents in the non-lipophilic polyphenol extract were the most effective at protecting hepatocytes against hydroperoxide induced hepatocyte oxidative stress and in protecting against dicarbonyl induced cytotoxicity; (b) catechins, the major polyphenol in the extract, were also effective at preventing GO or MGO cytotoxicity likely by trapping GO and MGO and/or rescuing hepatocytes from protein carbonylation.

Characterization of polyphenols, lipids and dietary fibre from almond skins ( Amygdalus communis L.)

Almond skins and blanch water are underutilized by-products of the almond processing industry. Nevertheless, they contain exploitable components that may contribute to the health benefits associated with almond consumption. We have compared natural almond skin powder (NS) prepared by a novel freeze-thawing method with blanched almond skin powder (BS). Microstructural studies were carried out, and we analyzed both types of almond skin for phenolic compounds (by HPLC), lipids (by solvent extraction), proteins (by micro-Kjeldahl), and fibre content (by the enzymatic-gravimetric AOAC method). Antioxidant activity (by measuring the reduction of the 2,2-diphenyl-1-picrylhydrazyl radical) was also monitored. We identified a combination of flavonols, flavan-3-ols, hydroxybenzoic acids and flavanones in NS, BS and in industrially obtained blanch water (BW). As expected, the total phenolic content was higher in NS compared to BW and BS, although the latter showed high antioxidant properties. Almond skins had high fibre content as well as significant amounts of lipid; both of these components may be relevant to fermentation in the large intestine. In addition, the processing of almond skins and blanch water clearly has economic potential for lowering the environmental impact of waste fill and pollution.

The potential of near infrared reflectance spectroscopy (NIRS) for the estimation of agroindustrial compost quality

Composting is an environmentally friendly alternative for the recycling of organic wastes and its use is increasing in recent years. An exhaustive monitoring of the composting process and of the final compost characteristics is necessary to certify that the values of compost characteristics are within the limits established by the legislation in order to obtain a safe and marketable product. The analysis of these parameters on each composting batch in the commercial composting plant is time-consuming and expensive. So, their estimation in the composting facilities based on the use of near infrared reflectance spectroscopy (NIRS) could be an interesting approach in order to monitor compost quality. In this study, more than 300 samples from 20 different composting procedures were used to calibrate and validate the NIRS estimation of compost properties (pH, electrical conductivity (EC), total organic matter (TOM), total organic carbon (TOC), total nitrogen (TN) and C/N ratio, macronutrient contents (N, P, K) and potentially pollutant element concentrations (Fe, Cu, Mn and Zn)). The composts used were elaborated using different organic wastes from agroindustrial activities (GS: grape stalk; EGM: exhausted grape marc; GM: grape marc; V: vinasse; CJW: citrus juice waste; Alpeorujo: olive-oil waste; AS: almond skin; EP: exhausted peat; TSW: tomato soup waste; SMS: spent mushroom substrate) co-composted with manures (CM: cattle manure; PM: poultry manure) or urban wastes (SS: sewage sludge) The estimation results showed that the NIRS technique needs to be fitted to each element and property, using specific spectrum transformations, in order to achieve an acceptable accuracy in the prediction. However, excellent prediction results were obtained for TOM and TOC, successful calibrations for pH, EC, Fe and Mn, and moderately successful estimations for TN, C/N ratio, P, K, Cu and Zn.

In vitro evaluation of the prebiotic properties of almond skins (Amygdalus communisL.)

In this study we investigated the potential prebiotic effect of natural (NS) and blanched (BS) almond skins, the latter being a byproduct of the almond-processing industry. A full model of the gastrointestinal tract, including in vitro gastric and duodenal digestion, followed by colonic fermentation using mixed faecal bacterial cultures, was used. Both NS and BS significantly increased the population of bifidobacteria and Clostridium coccoides/Eubacterium rectale group, resulting in a prebiotic index (3.2 for BS and 3.3 for NS) that compared well with the commercial prebiotic fructo-oligosaccharides (4.2) at a 24-h incubation. No significant differences in the proportion of gut bacteria groups and in short-chain fatty acid production were detected between NS and BS, showing that polyphenols present in almond skins did not affect bacterial fermentation. In conclusion, we have shown that dietary fibre from almond skins altered the composition of gut bacteria and almond skins resulting from industrial blanching could be used as potential prebiotics.

Profile of Plasma and Urine Metabolites after the Intake of Almond [Prunus dulcis (Mill.) D.A. Webb] Polyphenols in Humans

Nut skins are considered to be a rich source of polyphenols and may be partially responsible for the numerous health effects associated with nut consumption. However, more bioavailability studies of nut skin polyphenols are needed to understand the health effects derived from nut consumption. The aim of the present study was to determine the profiles of both phase II and microbial-derived phenolic metabolites in plasma and urine samples before and after the intake of almond skin polyphenols by healthy human subjects (n = 2). Glucuronide, O-methyl glucuronide, sulfate, and O-methyl sulfate derivatives of (epi)catechin, as well as the glucuronide conjugates of naringenin and glucuronide and sulfate conjugates of isorhamnetin, were detected in plasma and urine samples after consumption of almond skin polyphenols. The main microbial-derived metabolites of flavanols, such as 5-(dihydroxyphenyl)-gamma-valerolactone and 5-(hydroxymethoxyphenyl)-gamma-valerolactone, were also detected in their glucuronide and sulfate forms. In addition, numerous metabolites derived from further microbial degradation of hydroxyphenylvalerolactones, including hydroxyphenylpropionic, hydroxyphenylacetic, hydroxycinnamic, hydroxybenzoic, and hydroxyhippuric acids, registered major changes in urine after the consumption of almond skin polyphenols. The urinary excretion of these microbial metabolites was estimated to account for a larger proportion of the total polyphenol ingested than phase II metabolites of (epi)catechin, indicating the important role of intestinal bacteria in the metabolism of highly polymerized almond skin polyphenols. To the authors' knowledge this study constitutes the most complete report of the absorption of almond skin polyphenols in humans.

Comparative Flavan-3-ol Profile and Antioxidant Capacity of Roasted Peanut, Hazelnut, and Almond Skins

In the present study, the flavan-3-ol composition and antioxidant capacity of roasted skins obtained from the industrial processing of three commonly consumed tree nuts (i.e., peanuts, hazelnuts, and almonds), as well as fractions containing low and high molecular weight (LMW and HMW) flavan-3-ols, were studied with the aim of assessing their potential as a source of flavonoids. Roasted peanut and hazelnut skins presented similar total phenolic contents, much higher than that of almond skins, but their flavan-3-ol profiles, as determined by LC-ESI-MS and MALDI-TOF MS, differed considerably. Peanut skins were low in monomeric flavan-3-ols (19%) in comparison to hazelnut (90%) and almond (89%) skins. On the other hand, polymeric flavan-3-ols in peanut and almond skins occurred as both A- and B-type proanthocyanidins, but in peanuts the A forms (up to DP12) were predominant, whereas in almonds the B forms (up to DP8) were more abundant. In contrast, hazelnuts were mainly constituted by B-type proanthocyanidins (up to DP9). The antioxidant capacity as determined by various methods (i.e., total antioxidant capacity, ORAC, DPPH test, and reducing power) was higher for whole extracts from roasted hazelnut and peanut skins than for almond skins; however, the antioxidant capacities of the HMW fraction of the three types of nut skins were equivalent despite their different compositions and DPs. Nevertheless, the large variation in flavan-3-ol concentration, structural composition, type of interflavan linkage, and DP found among the three types of nut skins suggests large difference in their expected in vivo biological activities.

A subchronic oral toxicity study of almond skins in rats

Almond skins have been suggested to have some potential benefits. To investigate the subchronic toxicity of almond skins, a 90-feeding study was conducted in rats. Sprague–Dawley rats were randomly divided into four groups (20 rats/sex/group) and received a diet containing 0%, 2.5%, 5.0% and 10% (w/w) almond skins for 90 days. Daily clinical observations and weekly measurement of body weights and food consumption were conducted. Ophthalmic examinations were performed at pre-test and termination. Blood samples were obtained on day 46 and day 91 for the measurement of hematology, coagulation and clinical chemistry parameters. Urine samples were collected on day 91 for urinalysis. Animals were euthanized for necropsy. Selected organs were weighted and recorded. Histological examination was performed on all tissues from animals in the control and high-dose groups. No mortality, body weight, ophthalmic abnormalities or treatment-related findings in clinical observations, hematology, coagulation, urinalysis parameters, macroscopic or microscopic examinations were observed. Differences between treated and control groups in weight gain, food consumption, clinical chemistry, and organ weight were not considered treatment-related. The no-observed-adverse-effect-level (NOAEL) for almond skins was considered to be 10% (w/w) for both genders (females, 9.7 g/kg body weight/day; males, 8.2 g/kg body weight/day).

Quantification of Almond Skin Polyphenols by Liquid Chromatography‐Mass Spectrometry

Reverse phase HPLC coupled to negative mode electrospray ionization (ESI) mass spectrometry (MS) was used to quantify 16 flavonoids and 2 phenolic acids from almond skin extracts. Calibration curves of standard compounds were run daily and daidzein was used as an internal standard. The inter-day relative standard deviation (RSD) of standard curve slopes ranged from 13% to 25% of the mean. On column (OC) limits of detection (LOD) for polyphenols ranged from 0.013 to 1.4 pmol, and flavonoid glycosides had a 7-fold greater sensitivity than aglycones. Limits of quantification were 0.043 to 2.7 pmol OC, with a mean of 0.58 pmol flavonoid OC. Mean inter-day RSD of polyphenols in almond skin extract was 6.8% with a range of 4% to 11%, and intra-day RSD was 2.4%. Liquid nitrogen (LN(2)) or hot water (HW) blanching was used to facilitate removal of the almond skins prior to extraction using assisted solvent extraction (ASE) or steeping with acidified aqueous methanol. Recovery of polyphenols was greatest in HW blanched almond extracts with a mean value of 2.1 mg/g skin. ASE and steeping extracted equivalent polyphenols, although ASE of LN(2) blanched skins yielded 52% more aglycones and 23% less flavonoid glycosides. However, the extraction methods did not alter flavonoid profile of HW blanched almond skins. The recovery of polyphenolic components that were spiked into almond skins before the steeping extraction was 97% on a mass basis. This LC-MS method presents a reliable means of quantifying almond polyphenols.

Extraction, Identification, and Quantification of Flavonoids and Phenolic Acids in Electron Beam‐Irradiated Almond Skin Powder

The effect of electron beam irradiation doses from 0 to 30 kGy on extraction yield and phenolic compounds was evaluated in almond skin phenolic extracts (ASPE). Total soluble phenols and distribution of phenolic compounds from acidified methanol ASPE and 52% methanol ASPE were quantified using Folin-Ciocalteau method, liquid chromatography with diode array and fluorescence detection, and negative ion electrospray-mass spectrometry. Electron beam irradiation increased extraction yield by as much as 23%, with the greatest increase observed in the acidified methanol ASPE. Irradiated samples extracted with acidified methanol also exhibited an increase in extractable phenols (Folin-Ciocalteau) and total HPLC-resolved phenolics at all irradiation doses. Samples extracted with 52% methanol exhibited an increase at 10 and 20 kGy, but a 31% decrease at 30 kGy. An increase in aglycones respective to their glycosides was not observed with irradiation. Therefore, the increase in phenolics was attributed to release of phenolics from their cellular matrix.

Harvest year and growing region but not processing affect flavonoid content and antioxidant capacity of California almond skins.

The consistency of the flavonoid content and antioxidant capacity of plant foods across growing regions and harvest years as well as the impact of processing has received little attention. We have characterized the influence of these factors in California almond skins on their total phenols (via the Folin‐Ciocalteu reaction), flavonoid profile (by LC‐MS), and Ferric Reducing Antioxidant Power (FRAP) value. The processing (fumigation, steam pasteurization, and dry roasting) of Butte, Carmel and Nonpareil almond varieties did not change their flavonoid content or FRAP value. Almonds harvested in 2006 and 2007 had 13% less flavonoids than in 2005, but their total phenols and FRAP values were unchanged. Almonds grown in southern California contained 21% less total flavonoids (5.50 mg/100 g) than those from northern California, with their lower content of kaempferol‐3‐O‐rutinoside (78%), naringenin‐7‐O‐glucoside (56%), epicatechin (34%), dihydrokaempferol (30%), naringenin (28%), and isorahamnetin‐3‐O‐rutinoside (18%). However, the ratio of individual to total flavonoids was not different between almonds grown in northern, central or southern California. Almonds from the southern region had 29% less total phenols but similar FRAP values compared to the northern region. Thus, growing region and harvest year affect the total phenolic and flavonoid content but not the antioxidant activity of almond skins.

Almond skins digestion: release of phytochemicals and gut health.

Almond skins (Amygdalus communis L.) contain high‐value components, such as dietary fibre and polyphenols. Here we describe the bioaccessibility of phytochemicals from almond skins during gastrointestinal (GI) digestion and the role of cell walls in regulating bioaccessibility. A dynamic gastric model of digestion which simulates the physical‐chemical processing of the stomach and accurately mimics both the transit time and the luminal content of the upper human gut was used to digest almond skins in vitro. No significant changes were observed in the sugar composition of the cell walls of almond skin after in vitro gastric or in vitro gastric + duodenal digestion, suggesting that no degradation of the dietary fibre had occurred. The decrease in the concentration of the major phenolics and flavonoids within the almond skins after digestion was used as a measure of their bioaccessibility in the GI tract. Under UV light, blue autofluorescence was emitted from the phenolics within the walls of the sclerenchyma cells, the lignified cells of the xylem, and from the cuticle overlying the nucellar layer. Phytochemicals from almond skins are bioavailable in the GI tract. The high dietary fibre content could be exploited for the potential health benefits of non‐glycaemic carbohydrate functional food preparations, mainly for gut health.This work has been funded by the Almond Board of California.

Inhibition of lipid oxidation in refrigerated and frozen salted raw minced chicken breasts with electron beam irradiated almond skin powder

Antioxidant effects of electron beam irradiated almond skin powder (ASP) in raw minced chicken breasts (MCB) during refrigerated and frozen storage were studied. MCB samples were treated with BHT, non-irradiated ASP (0 kGy), irradiated ASP (10 kGy, 20 kGy and 30 kGy) and compared to MCB without antioxidants. Colour was determined on initial and final day of analysis while conjugated dienes (CD), peroxide values (POV), TBARS and hexanal content were evaluated periodically for 12 days of refrigerated storage and seven months of frozen storage. ASP addition lowered L* values compared to MCB without ASP or BHT. During refrigerated storage, MCB containing ASP had decreased formation of lipid oxidation products ranging from 0 to 66%, 7 to 24%, 0 to 37% and 4 to 71% reduction in POV, CD, TBARS and hexanal content, respectively, as compared to MCB without antioxidants over duration of study. A 15–65%, 3–25%, 14–50% and 28–82% reduction in POV, CD, TBARS and hexanal content, respectively, for frozen MCB was detected.

In Vitro Activity of Almond Skin Polyphenols for Scavenging Free Radicals and Inducing Quinone Reductase

Observational studies and clinical trials suggest nut intake, including almonds, is associated with an enhancement in antioxidant defense and a reduction in the risk of cancer and cardiovascular disease. Almond skins are rich in polyphenols (ASP) that may contribute to these putative benefits. To assess their potential mechanisms of action, we tested the in vitro effect of ASP extracted with methanol (M) or a gastrointestinal juice mimic (GI) alone or in combination with vitamins C (VC) or E (VE) (1-10 micromol/L) on scavenging free radicals and inducing quinone reductase (QR). Flavonoid profiles from ASP-M and -GI extracts were different from one another. ASP-GI was more potent in scavenging HOCl and ONOO (-) radicals than ASP-M. In contrast, ASP-M increased and ASP-GI decreased QR activity in Hepa1c1c7 cells. Adding VC or VE to ASP produced a combination- and dose-dependent action on radical scavenging and QR induction. In comparison to their independent actions, ASP-M plus VC were less potent in scavenging DPPH, HOCl, ONOO (-), and O 2 (-) (*). However, the interaction between ASP-GI plus VC promoted their radical scavenging activity. Combining ASP-M plus VC resulted in a synergistic interaction, inducing QR activity, but ASP-GI plus VC had an antagonistic effect. On the basis of their total phenolic content, the measures of total antioxidant activity of ASP-M and -GI were comparable. Thus, in vitro, ASP act as antioxidants and induce QR activity, but these actions are dependent upon their dose, method of extraction, and interaction with antioxidant vitamins.

Electron beam irradiated almond skin powder inhibition of lipid oxidation in cooked salted ground chicken breast

Antioxidant ability of electron beam irradiated almond skin powder (ASP) in cooked refrigerated ground chicken breasts (GCB) was investigated. Phenolic compound identification, total phenols and metal binding ability was determined. GCB were treated with irradiated ASP at 10, 20 and 30 kGy and tested against a positive (with TBHQ) and negative control (GCB without ASP or TBHQ) for colour, conjugated dienes (CD), TBARS and hexanal content during one week of refrigerated storage. Irradiation had no effect on total phenols, but resulted in greater metal chelation. Addition of ASP decreased hunter L∗ value in GCB. The 10 kGy ASP decreased lipid oxidation to the greatest extent (35.5–52.3%, 44.0–84.0%, and 74.9–87.4% decreases in CD, TBARS and hexanal formation, respectively) as compared to the negative control over one week of refrigerated storage. In general, cooked refrigerated GCB with ASP had lower oxidation products as compared to the negative control.

Capillary liquid chromatography–mass spectrometry for the rapid identification and quantification of almond flavonoids

A rapid negative ion ESI high-performance capillary liquid chromatography–mass spectrometry method was developed to identify and quantify flavonoids (e.g., flavanols, flavonols, flavanones and glycosides). Fifteen standards and two varieties of almond skin extract powder (Carmel and Nonpareil) were used to demonstrate the chromatographic separation, reproducibility and accuracy of the method that employed a 150 mm × 0.3 mm ChromXP 3C18-EP-120 column. All standards eluted in less than 10 min, providing a 9–12× reduction in analysis time compared to existing methods (90–120 min). However, isomers (e.g., catechin/epicatechin and galactosides/glucosides) were not resolved and, therefore, identified and quantified collectively. RSDs for retention time and peak area reproducibility (mass spectrometry data) were <0.5% and <5.0%, respectively. Peak area reproducibility was greatly improved (from a RSD > 10%) after the implementation of a low-flow metal needle in the ESI source. Quantitation by mass spectrometry also afforded a % error less than 5% for most compounds.

Polyphenols and Antioxidant Properties of Almond Skins: Influence of Industrial Processing

Almond (Prunus dulcis[Mill.] D.A. Webb) skins have been proposed as a source of bioactive polyphenols. In this article, the phenolic composition and antioxidant activity of almond skins obtained from different processes (blanching [freeze-drying], blanching + drying, and roasting) were studied. A total of 31 phenolic compounds corresponding to flavan-3-ols (33% to 56% of the total of phenolic compounds identified), flavonol glycosides (9% to 36%), hydroxybenzoic acids and aldehydes (6% to 26%), flavonol aglycones (1.7% to 18%), flavanone glycosides (3% to 7.7%), flavanone aglycones (0.69% to 5.4%), hydroxycinnamic acids (0.65% to 2.6%), and dihydroflavonol aglycones (0% to 2.8%) were determined in the skins from 3 different varieties of almonds. The total contents of phenolic compounds identified were significantly (P < 0.05) higher (around 2-fold) in the roasted samples than in the blanched almonds (freeze-dried). Industrial drying (oven drying) of the blanched almond skins produced an increase (< 2-fold) in the contents of phenolic compounds, although the results were only statistically significant (P < 0.05) for some samples. The antioxidant activity (ORAC values) was higher for the roasted samples (0.803 to 1.08 mmol Trolox/g), followed by the samples subjected to blanching + drying (0.398 to 0.575 mmol Trolox/g) and then the blanched (freeze-dried) samples (0.331 to 0.451 mmol Trolox/g). Roasting is the most suitable type of industrial processing of almonds to obtain almond skin extracts with the greatest antioxidant capacity.

Ultrafiltration as alternative purification procedure for the characterization of low and high molecular-mass phenolics from almond skins

A combination of sample preparation (ultrafiltration) and analysis techniques is proposed for the characterization of complex phenolic mixtures such as extracts from almond ( Prunus dulcis (Mill.) D.A. Webb) skins. LC/ESI-MS analysis of the permeates obtained after ultrafiltration on semipermeable membranes (low molecular-mass phenolic fractions) allowed the identification of several benzoic acids and aldehydes, flavan-3-ol monomers and oligomers, and flavonol and flavanone glycosides in almond skins. MALDI-TOF and ESI-MS/MS analysis of the diafiltered concentrates (high molecular-mass phenolic fractions) demonstrated the presence of proanthocyanidin oligomers up to decamers, composed of (epi)afzelechin, (epi)catechin and (epi)gallocatechin units linked by C C bonds (type B) and by both C C and C O bonds (type A). This analytical protocol can be of utility in the study of low and high molecular-mass phenolic compounds in natural products.

Utilization of Electron Beam Irradiated Almond Skin Powder as a Natural Antioxidant in Ground Top Round Beef

Defatted Carmel variety almond skin powder (ASP) irradiated at 0, 10, 20, and 30 kGy was mixed with ground top round beef at 0.5% (w/w) and stored at 4 degrees C. Color stability, peroxide values (PV), conjugated dienes (CD), thiobarbituric acid reactive species (TBARS), and hexanal were determined periodically over a 2-wk period. The L values were not affected by time or treatment. Initially, the redness (a value) was higher for both the negative control with no ASP (a value of 21.83) and positive control with 0.01% BHT (a value of 22.33) compared to samples that contained the ASP (a values from 17.70 to 20.17) on day 1. This decrease in redness was attributed to the presence of the ASP. Similar to day 1, the a values were not significantly different between the 2 controls over the duration of the study. All the samples with ASP exhibited lower lipid oxidation when compared to the negative control, with greatest oxidation retardation observed at 20 and 30 kGy. Over the treatment period, a 13% to 85% reduction in PV and a 40% to 80% reduction in TBARS were observed in the sample with 30 kGy ASP compared to the negative control. Generally, PV and TBARS of samples with ASP decreased with an increase in irradiation dose. While a difference due to irradiation dose was not observed in CD and hexanal content, the values were significantly lower (P < 0.05) than the controls over time. This study demonstrates that almond skin power could be used to extend the shelf life of refrigerated ground raw beef.

Almond (Prunus dulcis (Mill.) D.A. Webb) Skins as a Potential Source of Bioactive Polyphenols

An exhaustive study of the phenolic composition of almond ( Prunus dulcis (Mill.) D.A. Webb) skins was carried out in order to evaluate their potential application as a functional food ingredient. Using the HPLC-DAD/ESI-MS technique, a total of 33 compounds corresponding to flavanols, flavonols, dihydroflavonols and flavanones, and other nonflavonoid compounds were identified. Peaks corresponding to another 23 structure-related compounds were also detected. MALDI-TOF MS was applied to characterize almond skin proanthocyanidins, revealing the existence of a series of A- and B-type procyanidins and propelargonidins up to heptamers, and A- and B-type prodelphinidins up to hexamers. Flavanols and flavonol glycosides were the most abundant phenolic compounds in almond skins, representing up to 38-57% and 14-35% of the total quantified phenolics, respectively. Due to their antioxidant properties, measured as oxygen-radical absorbance capacity (ORAC) at 0.398-0.500 mmol Trolox/g, almond skins can be considered as a value-added byproduct for elaborating dietary antioxidant ingredients.