Impact of post-harvest storage conditions on polyphenol composition and antioxidant activity in natural almonds
Background: Post-harvest storage of natural almonds is a critical step, as it can cause the onset of microbial contamination and modify polyphenolic composition of almond skin, potentially altering the antioxidant capacity and overall, the health effects of the native product. This study aims to evaluate the impact of different post-harvest storage conditions on the microbiological stability, polyphenolic profile, and antioxidant activity of natural almonds (Prunus dulcis cv. "Fascionello"). Methods: Natural almonds were obtained from Consorzio Mandorla di Avola and stored under three conditions: light exposure at room temperature (RT), dark at RT, and dark at 4°C, monitoring temperature and relative humidity. Samples were analyzed at four time points (T0, T3, T6, and T9 months). Microbiological stability was assessed using standard plate-counting techniques; polyphenolic content was determined through spectrophotometric assays and RP-LC-DAD-ESI-MS/MS analysis, whereas the antioxidant activity was evaluated using different spectrophotometric and spectrofluorimetric assays including DPPH, TEAC, FRAP, and ORAC assays. Chemometric analyses were performed to compare polyphenolic changes across different storage conditions over time. Results: Temperature remained stable with moderate variations, indicating a well-controlled environment, while humidity exhibits significant fluctuations, likely influenced by external factors. No significant microbial contamination was detected throughout storage, confirming the microbiological safety of natural almonds. The polyphenolic content significantly decreased within the first 3 months, particularly under dark conditions at RT. However, a recovery phase was observed at 6 months, with cold-stored almonds retaining the highest levels of total polyphenols and flavonoids. The antioxidant activity of almond skin extracts correlated with polyphenolic content, showing an initial decline followed by stabilization under refrigerated storage. Hierarchical clustering analyses highlighted distinct polyphenolic expression patterns based on storage conditions and time points. Conclusion: Post-harvest storage conditions significantly impact the polyphenolic profile and antioxidant properties of natural almonds. For short-term storage (≤6 months), RT with controlled light exposure is sufficient to preserve polyphenols, whereas cold and dark conditions are recommended to maintain bioactive compound stability and antioxidant potential for long-term storage (>6 months). These findings provide valuable insights for optimizing storage strategies in the food, nutraceutical, and pharmaceutical industries.
https://doi.org/10.3389/fnut.2025.1582434
Investigating the influence of pin-to-plate atmospheric cold plasma on the physiochemical, nutritional, and shelf-life study of two raisins varieties during storage
Cold plasma technology, a non-thermal food processing method, significantly enhances food quality and safety by modifying its physicochemical and nutritional attributes. Additionally, this treatment extends the shelf-life of food products, ensuring prolonged freshness and improved overall quality. The present study systematically examined the effect of cold plasma treatment on various attributes, including moisture content (MC), pH, hardness (H), antioxidant activity (AOA), total phenolic content (TPC), rehydration ratio (Rr), browning index (BI), and color difference (ΔE) in black raisins (BR) and golden raisins (GR). The comprehensive analysis delivers valuable insights into the transformative influences of cold plasma on the physicochemical and nutritional characteristics of these raisin varieties. A Box–Behnken experimental design (BBD) combined with response surface methodology (RSM) was used to determine the optimization of treatment time (5, 10 and 15 min) and voltage (10, 20 and 30 kV). The optimized time and voltage for black raisins was 10 kV with 15 min, whereas, for golden raisins, it was 20 kV with 10 min. Furthermore, the experimentation of shelf-life studies for both raisins illuminated the substantial impact of cold plasma treatment, notably enhancing H, Rr, BI, AOA and TPC. Concurrently, a decline in MC and pH was observed throughout the storage period. Furthermore, plasma treatment improved the quality of raisins by reducing the total mesophilic aerobic bacteria count as compared to untreated ones from 4.65–2.42 to 4.71–2.40 log CFU/g for BR and GR, respectively, and similar results were also noticed in mold and yeast count during the 15 days of storage period. However, Future research of this study should delve into long-term storage effects, scalability for commercial applications, and the underlying mechanisms driving these improvements in raisin quality.
https://doi.org/10.1007/s11694-024-02764-8
Acceleration of lipid oxidation in raw stored almond kernels in response to postharvest moisture exposure.
Background: Almonds are an important crop in California, and increased yields necessitate that dried in-hull almonds are stored in the field for longer periods increasing the potential for postharvest moisture exposure (e.g. rain, fog, etc.). Processors are increasingly drying these 'wet' almonds to a moisture content of <6% using low heat before the hulling and shelling process in order to reduce mechanical damage to the nutmeat. To date, there is no information on the impact that moisture exposure and drying prior to hulling and shelling, has on lipid oxidation and storage shelf life of raw almonds. Results: Raw almonds exposed to ≤8% moisture and subsequently dried (MEx) and almonds not exposed to moisture exposure (≤ 4% moisture; control) were stored under accelerated shelf-life conditions and evaluated monthly over 12 months for free fatty acids value (FFA), peroxide value (PV), and headspace volatiles. At 12 months of accelerated storage, MEx almonds have 1.4 times higher FFA and 3.5 times higher PV than the control indicating significant oxidative damage. MEx almonds also demonstrated higher levels of headspace volatile compounds related to lipid oxidation (i.e. hexanal, octanal, hexanoic acid) throughout storage. Conclusion: Drying almonds exposed to postharvest moisture prior to storage results in a higher degree of lipid oxidation during storage and a significant reduction in shelf life. https://doi.org/10.1002/jsfa.11452
Oxidative stability of a new peanut butter bite product.
Peanut butter continues to be a mainstay in the American diet, but in its current form, peanut butter lacks the convenience of other foods. A peanut butter bite snack food has been developed that is individually wrapped, high in protein, and made mostly from peanut butter. The target market for the product is the active, health-conscious segment of the population that wants a high-protein peanut butter snack that is easy to pack, carry, and eat. The objective of the current study was to evaluate the shelf life of peanut butter bites under different storage and packaging conditions and specifically to monitor oxidative stability of the samples over time. Peanut butter bite samples were prepared with three different levels of added antioxidant (vitamin E). Products were sealed in two different types of packaging (metallized polyethylene and plastic polyethylene) and were stored at two different temperatures to determine the rate of deterioration of the product under various conditions. Oxidative stability was evaluated using two different analytical methods (peroxide value and TBARS assay) to evaluate primary and secondary oxidation products over a six month time period. All treatments were conducted in triplicate. Results show that higher levels of vitamin E resulted in greater stability. As expected, oxidation proceeded more quickly under higher temperature storage conditions. A shelf stable individually wrapped peanut butter snack product may be appealing to a large audience and could result in an increase in the consumption of peanuts. https://doi.org/10.1155/2021/5528315
Biodegradable film for raisins packaging application: evaluation of physico-chemical characteristics and antioxidant potential.
The objective of this study was to evaluate the application of a biodegradable film, based on grape seed flour extract, for raisin packaging. Physico-chemical characteristics (moisture, total soluble solids, total acidity, pH), total phenolic content and antioxidant activity were evaluated during 182 days of storage at 20 °C, compared to a poly(ethylene) film packaging. After 182 days, the use of biodegradable film increased raisin moisture and pH, decreased total soluble solids and total acidity of raisin compared to the use of poly(ethylene) film. The total phenolic content and antioxidant activity of raisin packed in the biodegradable film were 60.0 and 51.8% higher, respectively, than in poly(ethylene) film. The results showed that the biodegradable film based on seed flour extract is a potential material for active packaging due its contribution to the maintenance of the antioxidant activity of raisin and can be used for their conservation. https://doi.org/10.1016/j.foodchem.2021.130538
Microbiomes of commercially-available pine nuts and sesame seeds
Metagenomic analysis of food is becoming more routine and can provide important information pertaining to the shelf life potential and the safety of these products. However, less information is available on the microbiomes associated with low water activity foods. Pine nuts and sesame seeds, and food products which contain these ingredients, have been associated with recalls due to contamination with bacterial foodborne pathogens. The objective of this study was to identify the microbial community of pine nuts and sesame seeds using targeted 16S rRNA sequencing technology. Ten different brands of each seed type were assessed, and core microbiomes were determined. A total of 21 and 16 unique taxa with proportional abundances >1% in at least one brand were identified in the pine nuts and sesame seeds, respectively. Members of the core pine nut microbiome included the genera Alishewanella, Aminivibrio, Mycoplasma, Streptococcus, and unassigned OTUs in the families of Desulfobacteraceae and Xanthomonadaceae. For sesame seeds, the core microbiome included Aminivibrio, Chryseolina, Okibacterium, and unassigned OTUs in the family Flavobacteriaceae. The microbiomes of these seeds revealed that these products are dominated by environmental bacterial genera commonly isolated from soil, water, and plants; bacterial genera containing species known as commensal organisms were also identified. Understanding these microbiomes can aid in the risk assessment of these products by identifying food spoilage potential and community members which may co-enrich with foodborne bacterial pathogens. https://doi.org/10.1371/journal.pone.0252605
Shelf-Life Evolution of the Fatty Acid Fingerprint in High-Quality Hazelnuts (Corylus avellana L.) Harvested in Different Geographical Regions
Hazelnuts are characterized by a relatively high abundance of oleic acid and poly-unsaturated fatty acids, which give this fruit a high nutritional value. As a counterbalance, such a lipid profile is more susceptible to autoxidation and/or degradation reactions under enzymatic catalysis. Lipid oxidation occurs on fatty acids (FAs), both esterified on triacylglycerols and in free form (after lipolysis), but with favorable kinetics on the latter. In this study, the quali-quantitative changes in FA profiles (both free and esterified) were monitored during the shelf life (time 0, 6, and 12 months) as a function of different drying and storage conditions and different cultivars and geographical areas. A derivatization/extraction procedure was performed to quantify the profile of free and esterified fatty acids accurately. The overall profile of the free and esterified fatty acids concurred to create a biological signature characteristic of the cultivar and of the harvest region. The free and esterified forms' characterization enabled the efficient monitoring of the effects of both the hydrolytic activity (increment in overall free fatty acids) and the oxidative process (decrease in unsaturated free fatty acids versus esterified fatty acids) over the 12 months of storage.
https://doi.org/10.3390/foods10030685
Survival of Listeria monocytogenes during storage on dried apples, strawberries, and raisins at 4° C and 23° C.
The survival of Listeria monocytogenes was assessed during long-term storage on three dried fruits: dried apples, raisins and dried strawberries. Using sand as a carrier, the dried fruits were dry-inoculated with a four-strain cocktail of L. monocytogenes to achieve numbers of 4.0 to 4.6 log CFU/g. The inoculated foods were stored at 4 °C, 25-81% relative humidity (RH) and 23 °C, 30-35% RH for 336 days. Colonies of L. monocytogenes could not be recovered from the dried apples after inoculation, i.e., day 0. Concentrations of L. monocytogenes decreased rapidly on the raisins and dried strawberries during storage at 23 °C, with enhanced survival observed at 4 °C. Linear rates of decline for populations of L. monocytogenes during storage at 4 °C on the raisins and dried strawberries were 0.1 and 0.2 log CFU/g/month, respectively. The relative distribution of the four L. monocytogenes strains making up the cocktail was determined by multiplex PCR at the beginning of storage and after 336 days on the dried fruits. At day 0, L. monocytogenes populations were predominantly composed of the serotype 1/2a and 3a strains on both the raisins and dried strawberries. After long-term storage at 4 °C, a relative decrease in serotype 1/2a was observed on both fruits, coupled with relative increases in the serotype 3a strain during storage on both fruits, in addition to the serotype 1/2b strain on the raisins. These results demonstrate that L. monocytogenes is rapidly inactivated during storage on raisins and dried strawberries at 23 °C, but it is capable of long-term survival at 4 °C. Improved knowledge on the survival of L. monocytogenes on these commodities is important for predictive modeling and can be used to better inform microbial health risk assessments.
Comparison of Microwave Short Time and Oven Heating Pretreatment on Crystallization of Raisins.
Crystalline material can develop on the surface of raisins during storage and transport, affecting the final acceptability of the product. In this work, a mild thermal pretreatment was applied to raisins to melt the pre-existing crystals and the effect of such thermal treatments on the development of crystals over a storage period was investigated. The raisins selected for this study were of the Thompson seedless variety from one Chilean company. The thermal pretreatment of raisins at 50 °C and 70 °C for 20 min in an oven and microwave (800 W) irradiation for 15 s resulted in a reduction in the percentage of crystallized raisins (w/w) from more than 50% in the control samples to less than 10% after 35 days of storage at 15 and 25 °C in a 57% relative humidity environment. The results showed that some textural parameters, such as cohesiveness and chewiness, were not affected by thermal treatment and were independent of storage temperature.
The Occurrence of Aflatoxins in Nuts and Dry Nuts Packed in Four Different Plastic Packaging from the Romanian Market.
Mycotoxins are secondary metabolites produced by various fungi. A very important category of mycotoxins are aflatoxins, considered to be the most dangerous in humans. Aflatoxin B1, well known as a favorable factor in the occurrence of hepatocellular carcinoma in humans, is the most controversial of all mycotoxins. Aflatoxins, found in naturally contaminated food, are resistant to degradation by heat. Current food processing practices and conventional storage conditions do not completely eliminate aflatoxin contamination from the food supply chain. Long storage food products-such as peanuts, pistachio, nuts in general, and dried fruits-are susceptible to aflatoxins contamination. The type of plastic material can influence the concentration of aflatoxins during storage due to the permeability to gas and moisture exchange with the external milieu. Nuts in general and dried fruits are consumed in large quantities worldwide. Therefore, herein we investigated the effect of plastic material on the total aflatoxins and aflatoxin B1 content in 64 samples of nuts and dried fruits packed and stored in low-density polyethylene (LDPE), polypropylene (PP), polyethylene (PE), and polyethylene terephthalate (PET). The method consisted in a cleanup procedure using immunoaffinity columns coupled with RIDASCREEN FAST immunoenzymatic competitive assays based on the ELISA technique. Collected data were subjected to statistical analysis and multiple comparisons tests were applied. From the total analyzed samples, 14.06% exceeded the maximum admitted European levels for total aflatoxins. The highest concentrations of total aflatoxins were obtained from samples packed in LDPE, followed by PP, PE, and PET. Aflatoxin B1 was detected in all samples packed in LDPE, PP, and PE. Most of the samples packed in PET had concentrations <1 µg/kg. These results indicate that nuts in general packed and stored in LDPE are more prone to contamination with aflatoxins, while PET is more suitable for maintaining the quality and safety of these products.