Influence of Postharvest UV-C Hormesis on the Bioactive Components of Tomato during Post-treatment Handling

Mature green tomato fruit exposed to a pre-determined hormetic dose of UV-C (3.7 kJ/m²) and untreated fruit (control) were stored at 13 °C and 95% relative humidity. After 10, 20, and 30 days of storage, fruits were randomly sampled and transferred to room temperature (23 °C) for 7 and 14 days to allow ripening. Edible pericarp was excised from the equatorial region for subsequent analyses of the antioxidant components. Ascorbic acid and total phenolic contents were higher in the UV-treated tomatoes, but UV treatment significantly reduced the lycopene content of the tomatoes. The UV treatment did not affect significantly the antioxidant activity of the hydrophilic extract, expressed as Trolox equivalent. Both storage and ripening period were found to affect positively all the bioactive components of tomato evaluated in this study. The results suggest the possible existence of a window of opportunity for the development of practices based on storage temperature and duration to preserve the beneficial effects expected from UV-C hormesis and to circumvent its negative impact on lycopene synthesis.     

Stability and Degradation Kinetics of Bioactive Compounds and Colour in Strawberry Jam during Storage

The effect of storage time and temperature on degradation of bioactive compounds such as ascorbic acid, anthocyanins, total phenols, colour and total antioxidant capacity of strawberry jam were investigated. The results indicated that lightness (L) value decreased significantly (p < 0.05) over 28 days of storage at 4 and 15 °C, with lower values measured at higher temperatures. Anthocyanins, ascorbic acid and colour degradation followed first-order kinetics where the rate constant increased with an increase in the temperature. The reaction rate constant (k) increased from 0.95 × 10⁻² day⁻¹ to 1.71 × 10⁻² day⁻¹ at 4 and 15 °C for anthocyanins. Similarly, k increased from 2.08 × 10⁻² day⁻¹ to 4.54 × 10⁻² day⁻¹ at 4 and 15 °C for ascorbic acid. In general, total antioxidant activity for strawberry jam samples stored for 28 days at 4 and 15 °C exhibited lower values as compared to control (day 0). The results showed greater stability of nutritional parameters at 4 °C compared to 15 °C.     

Effects of Lactic and Acetic Acid on Survival of Salmonella enteritidis During Refrigerated and Frozen Storage of Chicken Meats

Chicken leg and breast meat samples inoculated with Salmonella enteritidis [4–5 log most probable number (MPN)/cm²] were dipped into lactic acid (LA; 1% and 3%) and acetic acid (AA; 1% and 2%) solutions for 10 min. After packaging, samples were stored at 4 °C (10 days) or −18 °C (6 months). Immediately after dipping into 1% LA, 3% LA, 1% AA, and 2% AA solutions, S. enteritidis counts on leg meat samples were reduced by 0.75, 1.21, 0.85, and 0.95 log MPN/cm², while the reductions were 0.97, 1.72, 0.92, and 1.58 log MPN/cm² on breast meat samples, respectively. The differences between the water-washed control and the acid-treated groups for Salmonella counts were statistically significant (P < 0.05). Salmonella counts on leg meat samples treated with 1% LA, 1% AA, and 2% AA were reduced by 0.54–1.52 log MPN/cm² (P < 0.05) during storage at 4 °C. However, for the breast meat samples, only Salmonella counts of water-washed controls were significantly reduced during refrigerated storage (P < 0.05). S. enteritidis counts on organic acid-treated samples were reduced by 0.13–0.55 log MPN/cm² during storage at −18 °C for 6 months, while the reduction on the water-washed controls was 0.64 log MPN/cm². It can be concluded that lactic or acetic acid treatment could be useful especially for reducing the initial Salmonella contamination. On the other hand, this pathogen could survive on poultry meats during refrigerated and frozen storage even following lactic or acetic acid decontamination.     

Application of Catalytic Hydrogen Evolution in the Presence of Neonicotinoid Insecticide Clothianidin

Clothianidin, a new generation of pesticide, was determined in spiked tap water, apple juice, and soil by square-wave adsorptive stripping voltammetry. The method of determination is based on the hydrogen evolution reaction catalyzed by clothianidin at the hanging mercury drop electrode. The optimal signal was detected at −1.4 V versus Ag/AgCl in citrate buffer at pH 2.2. Various parameters such as pH, buffer concentration, frequency, amplitude, step potential, accumulation time, and potential were investigated to enhance the sensitivity of the determination. The optimal results were recorded at an accumulation potential of −0.35 V, accumulation time of 7 s, amplitude of 100 mV, frequency of 200 Hz, and step potential of 7 mV. The mechanism of catalytic hydrogen evolution was considered under experimental and theoretical conditions. This electroanalytical procedure enabled to determine clothianidin in the concentration range 9 × 10⁻⁹–4 × 10⁻⁶ mol L⁻¹ in supporting electrolyte and tap water, 1 × 10⁻⁷–4 × 10⁻⁶ mol L⁻¹ in diluted apple juice, and 2 × 10⁻⁷–1 × 10⁻⁶ mol L⁻¹ in soil. The detection and quantification limits in supporting electrolyte and diluted apple juice were found to be 2.6 × 10⁻⁹, 8.6 × 10⁻⁹ and 3 × 10⁻⁸, and 1 × 10⁻⁷ mol L⁻¹, respectively. A standard addition method was successfully used to determine clothianidin in spiked tap water, spiked apple juice, and spiked soil.     

Quality Characteristic and Shelf Life Studies of Deep-Fried Snack Prepared from Rice Brokens and Legumes By-Product

Legumes and cereal by-product flours were formulated into six of deep-fried snacks, which were evaluated for their physicochemical and sensory properties. Shelf life was analyzed for chemical parameters including: moisture gain, free fatty acid (FFA), and peroxide value (PV) at time intervals of 5 days along with organoleptic evaluation at the beginning and after 5, 10, 15, 20, 25, and 30 days of storage at room temperature (29 ± 2.0 °C) and relative humidity (67 ± 2.5%). A strong negative correlation (−0.83) was observed between the bulk density and the expansion ratio of the products. During storage moisture gain, FFA and PV increased linearly (R ² > 0.92). The results of organoleptic evaluation of all six fried snacks showed that there was no consistent pattern for sensory attributes. The maximum shelf life of the products was 24 days under the storage conditions studied.     

Effects of postharvest UV‐C treatment on carotenoids and phenolic compounds of vine‐ripe tomatoes

Light red tomatoes were exposed to different doses of ultraviolet C (UV‐C) irradiation (1.0, 3.0 and 12.2 kJ m^?2). After treatment, the tomatoes were stored for 2 days at room temperature, and then analysed to determine the effect of irradiation on the main antioxidants, carotenoids and phenolic compounds and the results compared with the control samples. The lycopene content was found to have increased by 14% with respect to the control samples, while β‐carotene decreased. Cis‐isomers from lycopene also increased when the tomatoes were exposed to irradiation for more than 3 h. UV‐C irradiation also had a positive effect on total phenolic compounds; however, the same effect was not observed in the individually analysed phenolic compounds. While chlorogenic and ferulic acids increased in content, naringenin and rutin contents decreased. These results suggest that UV‐C irradiation of tomatoes could improve the beneficial effect of red tomatoes for human health by increasing the levels of certain bioactive compounds; it could also be used to obtain higher content of bioavailability components, such as cis‐isomers from lycopene.     

Electrochemical Determination of Phenothrin in Agricultural Formulations, Vegetables, and Storage Bags of Wheat and Rice by Differential Pulse Adsorptive Stripping Voltammetry (DP-AdSV)

An electroanalytical method has been developed for the determination of the pesticide phenothrin by differential pulse adsorptive stripping voltammetry on a hanging mercury drop electrode in universal buffer as supporting electrolyte. The best adsorption conditions were found to be pH 6.0, an accumulation potential of −0.6 V, and an accumulation time of 75 s. Effects of stirring rate, scan rate, pulse amplitude, and purge time were examined for the optimization of instrumental conditions. Calibration curve is linear in the range 2 × 10⁻⁹ to 2 × 10⁻⁷ mol l⁻¹ with a detection limit of 1.9 × 10⁻¹⁰ mol l⁻¹. The correlation coefficient and relative standard deviation were 0.995% and 1.1%. The method is applied to the determination of the phenothrin in agricultural formulations, vegetables, and storage bags of wheat and rice under Food Corporation of India’s storage system.     

Spectrophotometric Determination of Trace Nitrite with Brilliant Cresyl Blue Using β-Cyclodextrin as a Sensitizer

A simple and sensitive spectrophotometric method for determination of nitrite has been described. The method is based on the oxidation of brilliant cresyl blue (BCB) by nitrite in acidic medium, which results in the decrease in absorbance at 636 nm. The decrease in absorbance is directly proportional to nitrite concentration obeying Beer’s law. The sensitivity is largely enhanced in the presence of β-cyclodextrin (β-CD) because of inclusion complexation. It was calculated that β-CD and BCB could form 1:1 inclusion complexation with a formation constant of 546.6 L/mol. Linear calibration graphs were obtained for 0.02 × 10⁻³–0.8 × 10⁻³ g/L sodium nitrite at 636 nm. The detection limit for the analytical procedure was 4.0 × 10⁻⁶ g/L sodium nitrite. The relative standard deviation for determination of 0.1 × 10⁻³ g/L and 0.5 × 10⁻³ g/L sodium nitrite were 0.69% and 0.38%, for ten determinations, respectively. Twenty-two coexistent ions or species were examined, and no serious interference for most of ions was observed. The method has been applied to determine nitrite in water and vegetable samples with satisfactory results.     

A RESEARCH NOTE: SHELF‐LIFE OF LITE SYRUP AFTER OPENING AND STORAGE AT ROOM OR REFRIGERATED TEMPERATURE1

The shelf‐life of lite syrup after opening and storage at room temperature (25‐27C) or refrigerated (4‐5C) was studied to determine the physical, chemical and microbiological changes in the product with time. Bottles of lite syrup were sampled at time 0 (initial opening) and during storage at days 7, 21, 28, 60, 90, 150, and 180. Color, water activity, pH, moisture content, viscosity, and ^oBrix were determined. Microbial analyses included coliform, standard, and yeast and mold plate counts. Color, water activity, pH, and moisture content did not change during 180 days of storage. Viscosity and ^oBrix values dropped with time, and microbial counts remained insignificant (p>0.05). Overall, lite syrup stored 180 days at room temperature (25‐27C) was comparable in quality to that stored at refrigerated (4‐5C) temperature.     

Prediction of Drying Characteristics of Pomegranate Arils

The thin-layer drying characteristics of pomegranate arils were investigated at the temperature of 55, 65 and 75°C, and the thin-layer drying models were used to fit the drying data. The increase in drying air temperature resulted in a decrease in drying time. Five different thin-layer drying models were used to predict the drying characteristics. The Midilli et al. model showed a better fit to experimental drying data as compared to other models. Effective moisture diffusivities were calculated based on the diffusion equation for a spherical shape using Fick’s second law, and varied from 9.373 × 10⁻¹¹ to 3.429 × 10⁻¹⁰ m²/s over the temperature range. Moisture diffusivity values increased as air temperature was increased. The dependence of moisture diffusivity on temperature was described by an Arrhenius-type equation. The activation energies of control and pre-treated samples were determined to be 49.7 and 40.1 kJ/mol, respectively.     

Mathematical Modeling and Experimental Study on Thin-Layer Vacuum Drying of Ginger (Zingiber Officinale R.) Slices

The vacuum-drying characteristics of ginger (Zingiber officinale R.) slices were investigated. Drying experiments were carried out at a constant chamber pressure of 8 kPa, and at four different drying temperatures (40 °C, 50 °C, 60 °C, and 65 °C).The effects of drying temperature on the drying rate and moisture ratio of the ginger samples were evaluated. Efficient model for describing the vacuum-drying process was chosen by fitting five commonly used drying models and a suggested polynomial was fitted to the experimental data. The effective moisture diffusivity and activation energy were calculated using an infinite series solution of Fick’s diffusion equation. The results showed that increasing drying temperature accelerated the vacuum-drying process. All drying experiments had only falling rate period. The goodness of fit tests indicated that the proposed two-term exponential model gave the best fit to experimental results among the five tested drying models. The average effective diffusivity values varied from 1.859 × 10⁻⁸ to 4.777 × 10⁻⁸ m²/s over the temperature range. The temperature dependence of the effective moisture diffusivity for the vacuum drying of the ginger samples was satisfactorily described by an Arrhenius-type relationship with activation energy value of 35.675 kJ/mol within 40–65 °C temperature range.     

Kinetics of Mass Transfer in Microwave Precooked and Deep-Fat Fried Ostrich Meat Plates

The aim of this study was to evaluate the effect of microwave precooking on mass transfer during deep-fat frying of ostrich meat plates. The influence of microwave power level, frying temperature, and time on mass transfer was determined. Among all treatments, the plates being precooked at 5.23 W/g of microwave power and then deep-fat fried at 135 °C had the minimum fat content. The effective moisture diffusivity ranged between 1.47 × 10⁻⁸ and 4.17 × 10⁻⁸ m²/s. Fat transfer rate constant was in the range of 0.024 and 19.708 s⁻¹. The activation energy obtained from Arrhenius plot for the effective moisture diffusivity ranged between 38.84 and 51.07 kJ/mol.     

Water Diffusion and Concentration Profiles During Osmodehydration and Storage of Apple Tissue

The objective of this work was to study the mobility of water and sucrose during osmotic dehydration and storage of apple tissue and to conduct an analysis of the behavior of the effective diffusion coefficients determined from concentration profiles. Osmotic dehydration (OD) of apple was carried out at 40°C for 1 h, and the solution: sample ratio was 20:1 (w/w). Samples of 20-mm diameter were extracted from the dehydrated apple immediately after the OD process and after 4 and 24 h of storage at 25 °C. Moisture of these samples and soluble solids content were analyzed. Our results showed, after 1 h of OD, the outer layer of the apple sample lost 0.37 kg water/kg apple and gained 0.30 kg sucrose/kg apple. These values decreased toward the internal layers of the apple. A fine layer of greatly dehydrated cells was formed on the surface around the sample, which determined the mass transfer rate in the whole tissue. Smaller mass transport rates were observed in the development of concentration profiles during storage. Diffusion coefficients obtained for the outer layer after 1 h of OD were 1.53 × 10⁻¹⁰ and 1.05 × 10⁻¹⁰ m²/s for water and sucrose, respectively. The analysis of compositional profiles developed during osmodehydration was a useful tool to get a better understanding of the changes in the water activity of the outer layer of the apple tissue.     

A Sensitive, Selective New Analytical Reagent, 2, 6-Diacetylpyridine bis-4-phenyl-3-thiosemicarbazone for Extractive Spectrophotometric Determination of Mo(VI) in Food Samples

Synthesized a new reagent 2, 6-Diacetylpyridine bis-4-phenyl-3-thiosemicarbazone (2, 6-DAPBPTSC) characterized and is proposed as a sensitive and selective analytical reagent for the extractive spectrophotometric determination of molybdenum(VI) at pH 3.5 to form a yellowish orange colored 1:1 chelate complex. The absorbance was measured at a maximum wavelength, 500 nm. This method obeys Beer’s law in the concentration range 0.90–9.00 μg mL⁻¹ and the correlation coefficient of Mo(VI)–2,6-DAPBPTSC complex is 0.954, which indicates an adequate linearity between the two variables with good molar absorptivity and Sandell’s sensitivity, 1.212 × 10⁴ L mol⁻¹cm⁻¹, 0.0079 μg cm⁻², respectively. The precision and accuracy of the method is checked with calculation of relative standard deviation (n = 5), 0.894% and the detection limit value is 0.0056 μg mL⁻¹. The instability constant of the method has been calculated by Asmus’ method as 6.476 × 10^–5, at room temperature. The interfering effect of various cations and anions has also been studied. The method was successfully applied for the determination of Mo(VI) in food and water samples. The validity of the present method was evaluated in terms of Student ‘t’ test and Variance ‘f’ test, which indicates the significance of the present method an inter comparison of the experimental values, using atomic absorption spectrometer.     

The Application of NIR FT-Raman Spectroscopy to Monitor Starch Retrogradation and Crumb Firmness in Semolina Bread

In this study, the potential application of near-infrared (NIR) Fourier-transform (FT)-Raman spectroscopy to monitor starch retrogradation in stored bread crumb was investigated. Semolina-based bread was made and cut into slices, which were stored under controlled conditions in sealed plastic bags. The aging of the bread crumb was monitored by both NIR FT-Raman spectroscopy and a texture analysis over a period of 20 days. Two-dimensional correlation analysis in the spectral range of 390–975 cm⁻¹ revealed characteristic differences among the spectra collected over time for bands that peaked at 480, 765, and 850 cm⁻¹. The band at 480 cm⁻¹ is studied here in detail. During the storage, the peak frequency of this band shifted towards lower wavenumbers, and its full width at half height decreased. Both of these parameters are highly correlated (R ² = 0.921 and R ² = 0.949, respectively) to crumb hardness measured by the texture analyzer.     

Rapid Non-destructive Detection of Spoilage of Intact Chicken Breast Muscle Using Near-infrared and Fourier Transform Mid-infrared Spectroscopy and Multivariate Statistics

Near-infrared (NIR) transflectance and Fourier transform-infrared (FT-IR) attenuated total reflectance spectra of intact chicken breast muscle packed under aerobic conditions and stored at 4° for 14 days were collected and investigated for their potential use in rapid non-destructive detection of spoilage. Multiplicative scatter correction-transformed NIR and standard normal variate-transformed FT-IR spectra were analysed using principal component analysis (PCA), partial least-squares discriminant analysis (PLS2-DA) and outer product analysis (OPA). PCA and PLS2-DA regression failed to completely discriminate between days 0 and 4 samples (total viable count (TVC) days 0 and 4 = 5.23 and 6.75 log₁₀ cfu g⁻¹) which had bacterial loads smaller than the accepted levels (8 log₁₀ cfu g⁻¹) of sensory spoilage detection but classified correctly days 8 and 14 samples (TVC days 8 and 14 = 9.61 and 10.37 log₁₀ cfu g⁻¹). OPA performed on both NIR and FT-IR datasets revealed several correlations that highlight the effect of proteolysis in influencing the spectra. These correlations indicate that increase in free amino acids and peptides could be the main factor in the discrimination of intact chicken breast muscle. This investigation suggests that NIR and FT-IR spectroscopy can become useful, rapid, non-destructive tools for spoilage detection.     

Hot Air Puffing Kinetics for Soy-fortified Wheat-based Ready-to-Eat (RTE) Snacks

The soy-fortified wheat-based flat cold extrudate, after requisite steaming, was puffed in hot air using the high-temperature short-time (HTST) whirling-bed puffing system. The hot-air puffing was conducted at five different hot air temperatures, 200 to 240 °C at constant fluidizing air velocity of 3.95 m s⁻¹ for 50 s of puffing time. The initial moisture of sample was 0.4617 kg kg⁻¹ dm. The already existing 15 different thin layer-drying models were applied to determine the hot air puffing kinetics, based on puffing temperatures. It was found that the Page model could represent hot air puffing kinetics of the steamed flat cold extrudate within 99.3% accuracy. The effective diffusivity was found to be between 1.15623 × 10⁻⁹ and 2.58631 × 10⁻⁹ m² s⁻¹ for steamed flat cold extrudate in the temperature range of 200 to 240 °C. The activation energy for diffusion was found to be 2,341.824 kJ kg⁻¹. The optimum puffing conditions with respect to expansion ratio (ER) and sensory color score were found at puffing temperature of 220 °C and puffing time of 30 s. The variation in ER for the product was found to follow a linear relationship with moisture content of steamed flat cold extrudate during puffing. The Dincer Number for steamed flat cold extrudate puffed in fluidizing air at temperature 220 °C and 3.95 m s⁻¹ velocity was determined to be 276,223.8. This Dincer Number was used to predict the puffing time required to achieve predetermined moisture content of product. The prediction was found to be effective within 10% deviation from the values of experimental puffing time except during the initiation of puffing.     

Determination of Rosmarinic Acid by High-Performance Liquid Chromatography and Its Application to Certain Salvia Species and Rosemary

This study describes a method development for the determination of rosmarinic acid (RA) by using a gradient high-performance liquid chromatography (HPLC) and its application to certain plant materials. The analysis was performed by utilizing a two solvents system [A: methanol/water/formic acid (10:88:2; v:v:v); B: methanol/water/formic acid (90:8:2; v:v:v)] on a reverse-phase column. The flow rate and injection volume were 1 ml min⁻¹ and 10 μl, respectively. Signals were detected at 280 nm. In addition, an internal standard (IS) technique was applied for the analysis of RA to increase precision, and propylparaben was employed for this purpose. The repeatability results as RSD% were 1.66, 1.17 and 1.26 for intra-day and 1.38 was for inter-day with the employment of (3.67 × 10⁻⁵ M) RA. A limit of linearity (LOL) was observed in a wide (1.13 × 10⁻⁵–5.65 × 10⁻⁴ M) concentration range. Linearity parameters were also examined in the range of 5.95 × 10⁻⁶–7.14 × 10⁻⁵ M RA, and very good correlation was observed. The limit of detection (LOD) and limit of quantification (LOQ) (for inter-day) were 1.60 × 10⁻⁶ M (signal/noise [S/N] = 3.3) and 4.80 × 10⁻⁶ M (S/N = 10), respectively. The method was applied to the extracts of certain Lamiaceae plants (Salvia candidissima Vahl. subsp. candidissima, S. sclarea L., S. verticillata L. subsp. verticillata and R. officinalis L.), and reasonable results were obtained.     

Physicochemical and Enzymatic Properties of Five Kiwifruit Cultivars during Cold Storage

Samples of Abbot, Alison, Bruno, Monty, and Hayward cultivars of kiwifruit (Actinidia deliciosa) were obtained from the Iran Research Center of Citrus (Tonekabon, located in north of Iran) and their physicochemical properties were studied during cold storage (at T = 1 ± 1 °C, RH = 80 ± 5%) at 0-, 9-, and 18-week intervals. The mean chemical composition of the fruits were as follows: ash = 0.66–0.96%, moisture = 75.2–84.7%, starch = 0.3–7.0%, and ascorbic acid = 54.8–261.0; K = 125.0–372.0 mg 100 g⁻¹ fresh weight, Mg = 18.0–32.0 mg 100 g⁻¹ fresh weight, Na = 1.4–3.1 mg 100 g⁻¹ fresh weight, Fe = 0.17–0.52 mg 100 g⁻¹ fresh weight, Cu = 0.04–0.24 mg 100 g⁻¹ fresh weight, Zn = 0.16–0.49 mg 100 g⁻¹ fresh weight, Mn = 0.04–0.10 mg 100 g⁻¹ fresh weight, and P = 25.2–49.3 mg 100 g⁻¹ fresh weight; glucose = 0.7–2.39%, fructose = 1.20–3.13%, and sucrose = 0.0–5.8%. At the same time, the values of the parameters °Brix = 6.5–14.8% and acidity = 1.8–2.5% of the studied cultivars (mutual effects of cultivar and storage time) were investigated. The increase in peroxidase (POX = 0.0–6.65 U ml⁻¹) and the decrease in pectinesterase (PE; poor activity to 0) activities were also determined. The statistical analysis showed that the Bruno cultivar had the highest content of ascorbic acid (115.0–261.0 mg 100 g⁻¹ fresh weight), which is an important compound in fruits during storage, while Hayward had the best overall quality particularly with regards to its resistance to softening. This study confirms that long-term cold storage at 1 ± 1 °C and 80 ± 5% RH is suitable for maintaining the highest quality of Iranian grown cultivars of kiwifruit.     

HPLC of proteose peptones for evaluating ageing of packaged pasteurized milk

The proteolysis of casein (CN) occurring in packaged pasteurized milk (PM) during refrigerated storage was studied with relation to hygienic and microbiological characteristics of starting raw milk. Six batches of raw milk having standard plate count (SPC) from 1.5×10⁴ to 2.5×10⁵ cfu mL⁻¹ and somatic cell count (SCC) from 1.6×10⁵ to 4.4×10⁵ units mL⁻¹ were pasteurized (73 °C for 15 s), packaged and stored at 4 °C for 12 days. Capillary zone electrophoresis of CN showed breakdown of β-CN in all PM samples during storage. An HPLC method for monitoring proteose peptones (PP) formation was developed. Level of PP in PM samples increased, with keeping time from 667–789 to 947–1383 mg L⁻¹ and PP formation was significantly (P<0.05) related to SCC of starting raw milk. Electrospray ionization–mass spectrometry showed that PP were mainly represented by PP-5 from either A¹ or A² variants of β-CN. Five commercial samples of PM were analysed for PP formation during 14-day storage at 4 °C. Commercial samples prepared by microfiltration process or bactofugation combined with pasteurization showed the slowest formation of PP. The effect of storage temperature on PP formation was evaluated by keeping a conventional PM sample at either 8 or 12 °C for 12 days. Proteolysis of all major CNs upon action of plasmin and bacterial proteinases was observed under these conditions. PP level thus proves to be a reliable analytical index for evaluating the ageing of packaged PM during refrigerated storage.