Phloridzin and other phytochemicals in apple pomace: Stability evaluation upon dehydration and storage of dried product

Apple pomace (mixed Red Delicious and Golden Delicious varieties) obtained from the industrial production of puree was both vacuum-dried at 40 °C and air-dried at 60 °C, ground and stored at water activity (a_w) in the range 0.11–0.75, for 9 months, at 30 °C. The aims were to investigate the effect of drying and long-term storage on phytochemical contents. Air-drying at 60 °C was better than vacuum-drying at 40 °C in terms of anthocyanin and flavanol retention; no adverse effect of drying was observed for flavonols, dihydrochalcones and hydroxycinnamic acids. The maximum stability occurred for all apple phytochemicals at the lowest a_w. At a_w 0.75 degradation of all phytochemicals occurred with the following stability ranking: phloridzin > chlorogenic acid > quercetin 3-O-galactoside > epicatechin > procyanidin B2 and cyanidin 3-O-galactoside. A promising feature of pomace is its exclusive high content of phloridzin, which showed relatively high stability during long-term storage.     

Water activity and temperature effects on mycotoxin production by Alternaria alternata on a synthetic tomato medium

Alternaria spp. have been reported to be the most frequent fungal species invading tomatoes. Certain species, in particular the most common one, A. alternata, are capable of producing several mycotoxins in infected plants and in agricultural commodities. Alternariol (AOH), alternariol monomethyl ether (AME), and tenuazonic acid (TA) are some of the main Alternaria mycotoxins that can be found as contaminants of food. The objective of this study was to determine the effect of water activity (a_w, 0.904, 0.922, 0.954, and 0.982) and temperature (6, 15, 21 and 35 °C) on mycotoxin production on a synthetic tomato medium of a cocktail inoculum of five strains of A. alternata isolated from tomato fruits affected by Blackmould. The optimum AOH production occurred at 0.954 a_w after 28 days of incubation at 21 °C. A temperature of 21 °C was the most favourable for AOH synthesis at all a_w levels. The maximum concentration of AME was determined at 0.954 a_w and 35 °C. The optimum conditions for TA accumulation were 0.982 a_w and 21 °C. At the 0.904 a_w no growth or germination was registered at 6 °C and 15 °C over the whole incubation period. At 21 °C and 35 °C growth occurred slowly but none of the toxins were detected at this a_w level. In general, high a_w levels were favourable for mycotoxin production. None of the other toxins was detected at quantifiable levels at 6 °C after the whole incubation period. A storage temperature of 6 °C or below could be considered as safe for tomato fruits and high moisture tomato products (a_w > 0.95), in relation with Alternaria toxins. The results obtained here could be extrapolated to evaluate the risk of spoilage in tomato fruits and tomato products caused by this pathogen.     

Effects of light,temperature and water activity on the kinetics of lipoxidation in almond-based products

Lipoxidation in almond-derived products was investigated using the chemiluminescence (CL) and thiobarbituric acid-reactive substances (TBARS) methods to detect the first and later reaction products, respectively. The effects of light during storage at 5 °C, 22 °C and 40 °C were studied, as well as the effects of combined heat/water activity treatments in the 60–120 °C and 0.38–0.72 range. During storage, light was found to enhance the CL and TBARS values, and specific responses were observed in almond paste and the final Calisson product. During the heating of almond paste, as the initial water activity (a_w) increased, the CL rate constants increased during heating to 60 °C and 80 °C, but interestingly, these values decreased during further heating to 120 °C, whereas the maximum TBARS rate constants occurred at a_w 0.57 at all the heating temperatures tested. The activation energies, based on the CL and TBARS values, decreased specifically when the a_w increased from 0.38 to 0.72, giving overall values ranging from110 kJ mol⁻¹ to 60 kJ mol⁻¹. Likewise, in the same water activity range, the temperature-dependent rate constant enhancing factor (Q₁₀) decreased from 3.3 to 1.6.     

Influence of water activity and temperature on growth and mycotoxin production by Alternaria alternata on irradiated soya beans

The aim of this study was to determine the effects of water activity (a_w) (0.99-0.90), temperature (15, 25 and 30 °C) and their interactions on growth and alternariol (AOH) and alternariol monomethyl ether (AME) production by Alternaria alternata on irradiated soya beans. Maximum growth rates were obtained at 0.980 a_w and 25 °C. Minimum a_w level for growth was dependent on temperature. Both strains were able to grow at the lowest a_w assayed (0.90). Maximum amount of AOH was produced at 0.98 a_w but at different temperatures, 15 and 25 °C, for the strains RC 21 and RC 39 respectively. Maximum AME production was obtained at 0.98 a_w and 30 °C for both strains. The concentration range of both toxins varied considerably depending on a_w and temperature interactions. The two metabolites were produced over the temperature range 15 to 30 °C and a_w range 0.99 to 0.96. The limiting a_w for detectable mycotoxin production is slightly greater than that for growth. Two-dimensional profiles of a_w × temperature were developed from these data to identify areas where conditions indicate a significant risk from AOH and AME accumulation on soya bean. Knowledge of AOH and AME production under marginal or sub-optimal temperature and a_w conditions for growth can be important since improper storage conditions accompanied by elevated temperature and moisture content in the grain can favour further mycotoxin production and lead to reduction in grain quality. This could present a hazard if the grain is used for human consumption or animal feedstuff.     

Effect of water activity, temperature and incubation time on growth and ochratoxin A production by Aspergillus niger and Aspergillus carbonarius on maize kernels

The aim of this study was to determine the effects of water activity (a_w) (0.92-0.98), temperature (5-45 °C) and incubation time (5-60 days) on growth and ochratoxin A (OTA) production by Aspergillus niger and Aspergillus carbonarius on maize kernels using a simple method. Colony diameters of both strains at 0.92 a_w were significantly lower than those at 0.96 and 0.98 a_w levels. The optimum growth temperature range for A. niger was 25-40 °C and for A. carbonarius 20-35 °C. A. niger produced OTA from 15 to 40 °C, and the highest OTA level was recorded at 15 °C. The concentration of OTA produced at 0.92 a_w was significantly lower than those at 0.96 and 0.98 a_w. A. carbonarius produced OTA from 15 to 35 °C and the maximum concentration was achieved at 15 °C, although not differing statistically from the concentration detected at 20 °C. At 0.98 a_w the OTA concentration was significantly higher than at 0.96 and 0.92 a_w. Our results show that maize supports both growth and OTA production by A. niger and A. carbonarius. The studied strains were able to produce OTA in maize kernels from the fifth day of incubation over a wide range of temperatures and water availabilities. Although the limit of quantification of our method was higher than that required for the analysis of OTA in food commodities, it has proved to be a useful and rapid way to detect OTA production by fungi inoculated onto natural substrates, in a similar way as for pure culture. Both species could be a source of OTA in this cereal in temperate and tropical zones of the world.     

Distribution of zearalenone in malted barley fractions dependent on Fusarium graminearum growing conditions

Zearalenone (ZON) distribution was measured in main fractions of malted barley, dependent on incubation time (17, 26, 34 days), water activity (0.95 and 0.98) and temperature (20 °C and 30 °C). Malted samples were sterilised and inoculated with Fusarium graminearum. ZON levels were higher (p < 0.01) in bran and germ than flour under almost all growing conditions. Incubation at 30 °C resulted in generally lower ZON levels in germ and bran, regardless of a_w and incubation time. After 34 days, ZON levels in flour from samples that were incubated at the higher temperature rose significantly. At 20 °C ZON concentration showed a bell-shaped concentration profile with increasing incubation time in bran and germ, whilst ZON levels in flour increased at a_w 0.98 and dropped at the lower a_w. The results indicate the importance of storage conditions for ZON levels in commercially relevant grain fractions of malted barley and help predict existing mycotoxin levels or manipulate storage conditions to reduce ZON content.     

Effect of fenpropimorph, prochloraz and tebuconazole on growth and production of T-2 and HT-2 toxins by Fusarium langsethiae in oat-based medium

Fusarium langsethiae has been isolated from infected cereals in central and northern Europe where it has been identified in the last decade as the main species involved in the occurrence of high levels of T-2 and HT-2 toxins, mainly in oats. The efficacy of three fungicides (prochloraz, tebuconazole, fenpropimorph) for controlling growth of two strains of F. langsethiae isolated from oats was examined at 0.96 and 0.98 a_w at 15, 20 and 25 °C on oat-based media. The concentrations necessary for 50 and 90% growth inhibition (ED₅₀ and ED₉₀ values) were determined. The effect on the trichothecene type A mycotoxins T-2 and HT-2 was also determined. Without fungicides both strains grew faster at 0.98 than at 0.96 a_w and the influence of temperature on growth rates was 25 > 20 > 15 °C. Prochloraz and tebuconazole were more effective than fenpropimorph against F. langsethiae. Strain, temperature and type of fungicide significantly influenced the ED₅₀ and ED₉₀ values for growth. The concentration ranges under different environmental conditions were: prochloraz (0.03-0.1 and 0.3-1.5), tebuconazole (0.06-0.9 and 1.3-8.2), and fenpropimorph (22-59 and 125-215 mg l⁻¹). Production of T-2 and HT-2 toxins was influenced by temperature, a_w, type of fungicide and dose. Levels of T-2 were usually higher than those of HT-2 under the same conditions. The biosynthesis of T-2 toxin increased after 10 day incubation, but was reduced with decreasing temperature and increasing fungicide dose. At 0.98 a_w T-2 levels increased in cultures containing fenpropimorph while at 0.96 a_w the toxin concentrations increased in response to the other two fungicides. Low doses of prochloraz or tebuconazole enhanced toxin production when compared with untreated cultures for strain 2004-59 at 0.96 a_w and 20-25 °C. HT-2 was hardly detectable in the treatments with prochloraz or tebuconazole at 0.98 a_w. This is the first study on the effect of these anti-fungal compounds on control of growth of F. langsethiae and on production of T-2 and HT-2 toxins in oat-based media.     

Effect of antioxidants and competing mycoflora on Fusarium verticillioides and F. proliferatum populations and fumonisin production on maize grain

This study was carried out to determine the temporal effect of the antioxidants butylated hydroxyanisol (BHA) and propyl paraben (PP) at doses of 500 and 1000 μg/g on the growth of Fusarium verticillioides and F. proliferatum inoculated on natural maize grain in the presence of the competing mycoflora and fumonisin production at 0.98 and 0.95 water activity (a_w) over a 28-day storage period. The reduction in the log colony forming units (CFU) of Penicillium, Aspergillus and Fusarium populations was 10-100 fold depending on dose of BHA or PP, a_w and time. However, the populations of all three groups were higher at 0.98 a_w than 0.95 a_w. BHA at 500 μg/g and 0.95 a_w reduced the fumonisin content by 82% after 7-14 days incubation, but at the end of the experimental period the reduction was only 32%. A higher reduction in the level of fumonisin produced (77%) was achieved with BHA at 1000 μg/g after 28 days. PP at 500 and 1000 μg/g decreased fumonisin production throughout the incubation period in the drier treatment, but at 0.98 a_w control of toxin production was only achieved after 7-14 days. The reduction in the fumonisin levels could be due to the combined effect of antioxidants, and the competing mycoflora, mainly Aspergillus and Penicillium species.     

Evaluation of ability of ferulic acid to control growth and fumonisin production of Fusarium verticillioides and Fusarium proliferatum on maize based media

The aim of this study was to evaluate the efficacy of ferulic acid (1, 10, 20 and 25 mM) at different water activity (a_w) values (0.99, 0.98, 0.96 and 0.93) at 25 °C on growth and fumonisin production by Fusarium verticillioides and Fusarium proliferatum on maize based media. For both Fusarium species, the lag phase significantly decreased (p ≤ 0.001), and the growth rates increased (p ≤ 0.001) at the lowest ferulic acid concentration used (1 mM), regardless of the a_w. However, high doses of ferulic acid (10 to 25 mM) significantly reduced (p ≤ 0.001) the growth rate of both Fusarium species, regardless of the a_w. In general, growth rate inhibition increased as ferulic acid doses increased and as media a_w decreased. Fumonisin production profiles of both Fusarium species showed that low ferulic acid concentrations (1–10 mM) significantly increased (p ≤ 0.001) toxin production, regardless of the a_w. High doses of ferulic acid (20–25 mM) reduced fumonisin production, in comparison with the controls, by both Fusarium species but they were not statistically significant in most cases. The results show that the use of ferulic acid as a post-harvest strategy to reduce mycotoxin accumulation on maize needs to be discussed.     

Impact of controlled atmosphere on the stability of Dhakki dates

The dates equilibrated at water activity (a_w) of 0.52, 0.58 and 0.75 were stored at 40 °C for 4 months under the controlled atmosphere of nitrogen, oxygen and air. The samples were evaluated monthly for darkening, pH, and titratable acidity. The study indicates that the darkening and titratable acidity increased whereas the pH declined gradually during the storage. The change in quality appeared to be a function of storage atmosphere and water activity. Among all the investigated options, the sample stored under the nitrogen atmosphere at lowest water activity (0.52a_w) showed the greatest stability.     

Water migration mechanisms in amorphous powder material and related agglomeration propensity

The agglomeration phenomenon of amorphous particulate material is a major problem in the food industry. Currently, the glass transition temperature (T_g) is used as a fundamental parameter to describe and control agglomeration. Models are available that describe the kinetics of the agglomeration process as a function of the distance of the material from T_g (i.e. T − T_g). In practice these models are often not applied because they assume that the powder material is instantly in equilibrium with the humidity conditions of the environment and that solid mobility only occurs at T > T_g. Insights in the kinetics and mechanisms of water transport in powder material can help to better understand and control powder agglomeration. For this purpose, gravimetric step-change water sorption experiments were performed on maltodextrins as a function of the water activity a_w. The maltodextrins vary in dextrose equivalents (DE), particle size and morphology. The experimental results were compared with a Fickian diffusion model in order to understand the dependency of the transport mechanism on water concentration gradient and material relaxation. The water transport kinetics in the maltodextrins with low DE (i.e. 6) were well described by Fickian diffusion for low a_w, independently of particle size and morphology, until relaxation phenomena started to occur at an a_w corresponding to T − T_g = −20 °C. The importance of the matrix relaxation phenomena on the water transport mechanism increased with increasing DE (i.e. 29 and 32), not showing any relationship with the T_g. The results of this study indicate that the water migration mechanism is controlled by relaxation phenomena when the amorphous material is still far from the glass–rubber transition. The T − T_g at which the relaxation phenomena occur depends on the material. On the contrary, the T − T_g parameter could well describe the onset of agglomeration, independently from the material properties. Therefore, it can be concluded that within the conditions of this study, matrix relaxation occurring far below T_g did not affect the onset of agglomeration.     

Storage water activity affects flavor fade in high and normal oleic peanuts

Studies were conducted on roasted high oleic (HOP) and normal oleic peanuts (NOP) to investigate the effect of storage water activity on flavor changes. Peanuts were stored for 0–7 weeks at 0.19 and 0.60 water activities (a_w). Volatile flavor compounds were analyzed using solid phase microextraction–gas chromatography. HOP had better oxidative stability compared to NOP, which had peroxide values 7–10 times higher. Sensory evaluation showed HOP retained roasted peanutty characteristics and resisted off-flavor development during storage better than NOP. Pyrazines remained at higher levels after storage in HOP, which also formed lower levels of aldehydes. Oxidation and sensory changes were higher at low a_w.     

Kinetics of enthalpy relaxation of milk protein concentrate powder upon ageing and its effect on solubility

Kinetics of enthalpy relaxation of milk protein concentrate (MPC) powder upon short-term (up to 67 h) storage at 25 °C and a_w 0.85, and long-term (up to 48 days) storage at 25 °C and a range of a_w values (0–0.85) were studied by differential scanning calorimetry (DSC). The short-term study showed a rapid recovery of enthalpy for the first 48 h, followed by a slower steady increase with time. The non-exponential β parameter was calculated using the Kohlrausch–Williams–Watts function and found to be 0.39. Long-term storage showed that enthalpy relaxation depends on both storage period and water activity. The enthalpy value was much less for lower moisture content (mc) (a_w ? 0.23, mc ? 5.5%) than for higher mc (a_w ? 0.45, mc ? 8%) samples for a particular storage period. The results suggest that the presence of more water molecules, in close proximity to the protein surface facilitates kinetic unfreezing and subsequent motion of molecular segments of protein molecules towards thermodynamic equilibrium. Although de-ageing of stored samples did not reverse storage-induced solubility losses, the timescale of enthalpy relaxation was similar to that of solubility loss. It is suggested that enthalpy relaxation within stored samples allows structural rearrangements that are responsible for subsequent solubility decreases.     

Quality assessment of wild European eel (Anguilla anguilla) stored in ice

The quality assessment of wild European eel (Anguilla anguilla) stored in ice and in boxes without ice (3 ± 1 °C) was investigated by the sensory analysis, levels of nucleotide breakdown products and biogenic amines for up to 19 days. Sensory analysis was assessed using the Tasmanian Food Research Unit Scheme. K and related values (K_i, G, P, H and F_r) were used as freshness indicators. Linear regressions (r²) obtained from K, K_i, G, P, H and F_r were 0.95, 0.96, 0.83, 0.96, 0.99 and 0.96, respectively, for eel stored in ice whereas, for eel kept in boxes without ice, the values were 0.86, 0.86, 0.96, 0.91, 0.98 and 0.86, respectively. When eel stored in ice and in boxes without ice were considered at the limit of acceptability by assessors at ∼12–14 days and ∼5–7 days, respectively, the average K, K_i and P values were ∼70–85%, H values were ∼60% and F_r values were ∼10% for both storage conditions. The level of histamine exceeded the legal limit (5 mg/100 g fish) in eel stored without ice after 6–7 days and, in ice, after 13–14 days of storage, at which time eels were rejected by the sensory panel. The concentrations of biogenic amines were higher in eel stored in boxes without ice than in eel kept in ice. The levels of histamine in the muscle of eel kept in boxes without ice and in ice increased to the maximum levels of 17.9 mg/100 g on day 12 and 12.6 mg/100 g on day 19, respectively.     

Pre-processed spice mix formulation and changes in its quality during storage

Wet and dry spice and condiments of optimized quantities were pre-processed and mixed to prepare a spice mix formulation. The formulation was unit packed in 100 g quantities in glass bottles and held separately at 27±2 or 37±2 °C for 6 months. Freshly prepared spice mix contained (g/100 g) 6.8 moisture, 21.4 fat, 5.1 protein, 7.2 ash and 14.2 NaCl. Gradual decrease in pH from 4.0 to 3.7 and 4.0 to 3.6, increase in a_w from 0.52 to 0.54 and 0.52 to 0.57, increase in free fatty acid (FFA) values (as % oleic acid) from 0.14 to 0.56 and 0.14 to 0.58 and increase in thiobarbituric acid (TBA) values (mg malonaldehyde/kg sample) from 2.5 to 2.9 and 2.5 to 2.9 were noticed during storage at 27±2 or 37±2 °C respectively. Similarly decrease in Hunter L^* (lightness), a^* (redness) and b^* (yellowness) values were noted during the same period. Standard plate count (SPC), spore counts and staphylococci counts (log  cfu/g) were low, 4.0-4.7, 1.2-2.0 and 1.4-2.0, respectively, and yeast and moulds and coliforms could not be detected in all the samples throughout the storage period of 6 months. Two ready-to-serve products, viz., dhal fry and chicken fry prepared by using spice-mix stored for up to 6 months were judged acceptable as indicated by sensory quality scores of 6.8-7.9 (on a 9-point hedonic scale). The spice mix formulation prepared is useful in the preparation of varieties of vegetarian and non-vegetarian ready-to-serve products such as aloo mattar, gobi masala, mattar mushroom, kheema mattar, Mutton chilly fry, etc.     

Histamine production by Enterobacter aerogenes in tuna dumpling stuffing at various storage temperatures

Enterobacter aerogenes was studied for its growth, and promoting the formation of total volatile base nitrogen (TVBN) and histamine in tuna dumpling stuffing stored at various temperatures from −20 °C to 37 °C. The bacterial number rapidly increased in low (2.0 log CFU/g) or high (5.0 log CFU/g) inoculated concentrations at temperature above 15 °C and reached the highest bacterial count at 37 °C. In addition, the low spiked sample stored at 37 °C for 12 h and the high spiked sample stored at 25 and 37 °C for 12 h, formed histamine at above 50 mg/100 g of the potential hazard level in most illness cases. However, bacterial growth was controlled by cold storage of the samples at 4 °C or below, but histamine formation was stopped only by frozen storage. Once the frozen stuffing samples were thawed and stored at 25 °C, histamine started to accumulate rapidly.     

Cooking quality of faba bean after storage at high temperature and the role of lignins and other phenolics in bean hardening

Selected physical and chemical characteristics of faba beans (Vicia faba L.) cv. Fiesta were studied after 12 months storage at 5, 15, 25, 37, 45 or 50 °C (±2 °C) in relation to the hard-to-cook phenomenon. In comparison with control (seeds stored at 5 °C), seeds stored at 15 and 25 °C demonstrated non-significant (p?0.05) changes in most of the physical and chemical characteristics including hydration and swelling coefficients, acid detergent fibre, lignin and tannin contents, whereas seeds stored at ?37 °C demonstrated significant changes (p?0.05). Solutes and electrolytes leaching after 18 h soaking substantially increased with increased temperature. Faba bean hardness tested by the hard-to-cook test also increased substantially with increased storage temperature. After 8 h soaking followed by 2 h cooking, the puncture force required for seeds stored at 5 °C was 3.3 N seed⁻¹ whereas seeds stored at 50 °C required a much higher puncture force of 15.2 N seed⁻¹. There was a high negative correlation (r²=0.98) between storage temperature and cooking ability of faba bean. Substantial increases in acid detergent fibre and lignin contents occurred with increased storage temperatures. There was a three-fold increase in lignin content of faba bean stored at 50 °C compared to those stored at 5 °C and it was correlated with bean hardness (r²=0.98). Storage at high temperatures for 12 months led to a substantial reduction in total free phenolics especially in the testa and there was a greater reduction with increasing storage temperature. Reduction in free phenolics was negatively correlated (r²=0.75) with bean hardness.