Comparison of vacuum impregnation and soaking techniques for addition of the probiotic Lactobacillus acidophilus to minimally processed melon

This study aimed to evaluate the vacuum impregnation (VI) and soaking methods in the addition of Lactobacillus acidophilusLA‐3 to minimally processed melon (MPM). The melons were washed, sanitised in chlorine solution (200 mg L^?1), peeled and cutted into cubes. Lactobacillus acidophilusLA‐3 (1.4 × 10¹⁰ CFU g^?1) were added to the MPM through both techniques. The L. acidophilusLA‐3 count in MPM was similar to those commonly found in dairy products having probiotic claim, but VI was more efficient than soaking in maintaining the viability (8.61 and 7.98 Log CFU g^?1, respectively). The pH, acidity and soluble solids were not affected by probiotic culture and the incorporation technique; however, the VI affected the firmness of fruit. The MPM was within Brazilian standards for their microbiological characteristics. MPM may be used as a carrier of probiotic bacteria, being one more alternative for individuals who consume probiotic products.     

Combined Vacuum Impregnation and Electron‐Beam Irradiation Treatment to Extend the Storage Life of Sliced White Button Mushrooms (Agaricus bisporus)

This study assessed the application of an antibrowning solution using vacuum impregnation (VI) and then electron‐beam irradiation as a means to extend the shelf life of sliced white button mushrooms (Agaricus bisporus). A preliminary study helped to determine the best antibrowning solution and VI process parameters. Mushroom slices were impregnated with 2 g/100 g ascorbic acid + 1 g/100 g calcium lactate; 2 g/100 g citric acid + 1 g/100 g calcium lactate; 1 g/100 g chitosan + 1 g/100 g calcium lactate; and 1 g/100 g calcium lactate at different vacuum pressures and times and atmospheric restoration times. Selection of the antibrowning solution and VI parameters was based on texture and color of the mushroom slices. Next, the slices were irradiated at 1 kGy using a 1.35‐MeV e‐beam accelerator. Physicochemical, sensory, and microbial quality of mushrooms was monitored for 15 d at 4 °C. The best impregnation process in this study was 2 g/100 g ascorbic acid and 1 g/100 g calcium lactate at 50 mm Hg for 5 min and an atmospheric restoration time of 5 min. The control (untreated) samples suffered structural losses throughout storage. Only the vacuum impregnated‐irradiated samples had acceptable color by the end of storage. Sensory panelists consistently preferred the samples produced with VI and irradiation because exposure to ionizing radiation inhibited growth of spoilage microorganisms.     

Effect of silver carp (Hypophthalmichthys molitrix) muscle hydrolysates and fish skin hydrolysates on the quality of common carp (Cyprinus carpio) during 4 °C storage

Silver carp (Hypophthalmichthys molitrix) skin and muscle were hydrolysed, respectively, and then used as part of an edible coating to preserve fish. The effects of muscle and skin hydrolysates as edible coatings for shelf life extension of common carp (Cyprinus carpio) were evaluated over 18 days at 4 °C, by comparing these two treatments, a chitosan coating with muscle hydrolysate, chitosan alone, and an untreated control. All coatings were made up with 5% glycerol. The quality of the carp was assessed by using total volatile basic nitrogen (TVB‐N), total viable counts (TVC), thiobarbituric acid (TBA) and K value. Compared with the control group, the rate of increase in TVB‐N, TVC, TBA and K value of carp coated with fish skin hydrolysates, fish muscle hydrolysates and chitosan added to fish muscle hydrolysates were lower. According to the total viable counts, the storage life of fish with fish skin hydrolysates coatings and chitosan added fish muscle hydrolysates coatings were 16 days, 2 days longer than those with the chitosan coatings and twice as long as the control group.     

Effectiveness of gelatine and chitosan spray coating for extending shelf life of vacuum-packaged beef

The effects of applying gelatine (10%) and chitosan (1%) as spray coatings to extend the shelf life of vacuum-packaged beef was studied and compared against uncoated vacuum-packaged beef for up to 21 days. The impact of edible coatings on the water-holding properties of vacuum-packaged beef was investigated by LF-NMR together with physicochemical, microbiological and sensorial assessments. Chitosan coating significantly reduced lipid oxidation by ~30% to 36% and inhibited the growth of lactic acid bacteriaby ~ 1–2 log cfu compared to purge collected from uncoated and gelatine coated samples. It did not negatively affect the meat pH, tenderness and colour, and exhibited significantly higher sensorial acceptance compared to beef coated with gelatine. Both coatings were not effective in reducing purge loss in vacuum-packaged meat as the storage time increased. This study suggests that chitosan spray coating could be easily adapted to industrial plant settings as an antioxidant and antimicrobial application before carrying out meat vacuum packaging operation.     

Effectiveness of edible coatings combined with mild heat shocks on microbial spoilage and sensory quality of fresh cut broccoli (Brassica oleracea L.)

The use of edible coatings and mild heat shocks is proposed as postharvest treatments to prevent microbial deterioration of refrigerated broccoli. Minimally processed broccoli was coated with either chitosan or carboxymethyl-cellulose (CMC) combined or not with a previous application of a mild heat shock. The evolution of microbial populations (mesophilic, psycrotrophic, Enterobacteriaceae, molds and yeast, and lactic acid bacteria) was studied during 20 d of storage and fitted to Gompertz and logistic models. Results revealed that, at the end of the storage, chitosan coating significantly reduced all microbiological population counts, except lactic acid bacteria; while higher reduction was observed with chitosan coating combined with a heat shock treatment. A significant delay at the beginning of the exponential phase was observed for all the bacterial populations analyzed. On the other hand, CMC coating, with and without a previous thermal treatment, did not exert any antibacterial effect. Excellent agreement was found between experimental microbial counts and predicted values obtained from Gompertz and logistic models. Kinetic modeling was found to be valuable for prediction of microbiological shelf life of broccoli during storage. Results showed that the application of chitosan coating effectively maintained microbiological quality and extended shelf life of minimally processed broccoli. According to these results, the use of the edible chitosan coating alone or in combination with a heat mild shock appear to be a viable alternative for controlling microbiological growth and sensory attributes in minimally processed broccoli. PRACTICAL APPLICATION: The continuous consumer interest in high quality and food safety, combined with environmental concern has induced to the development and study of edible coatings that avoid the use of synthetic materials. The edible coatings, formed from generally recognized as safe materials, have the potential to reduce weight loss, respiration rate, and improve food appearance and integrity. It is one of the most effective methods to maintain food quality. On the other hand, heat treatments have been demonstrated to be effective as a nonchemical means of improving postharvest quality for a variety of horticultural products. The applications of mild heat shocks combined with edible coatings constitute an alternative for the natural preservation of crops for which the use of synthetic chemicals is objectionable.     

Effectiveness of antibrowning agents applied by vacuum impregnation on minimally processed pear

Different isotonic solutions containing antibrowning compounds (EDTA, 4-hexylresorcinol, citrate and ascorbate), combined or not with calcium lactate, were applied to minimally processed (MP) pear samples (cv. Blanquilla) by using the vacuum impregnation (VI) technique in order to reduce enzymatic browning. Vacuum impregnated samples were packaged and colour, mechanical properties, development of respiration gases and volatiles in the package headspace and microbial counts were monitored throughout storage at 4 °C. VI treatments with ascorbate solutions and calcium lactate were the most effective to extending the shelf life of MP pear. These treatments caused fewer changes in colour, mechanical properties and volatile composition and slowed microbial growth. Calcium lactate led to a better preservation in terms of mechanical parameters but had minor effects on colour development during cold storage.     

Reduction in the pH of vegetables by vacuum impregnation: A study on pepper

A method to decrease pH value in pepper slices employing vacuum was studied. The effects of relaxation time (10, 15 and 30 min), vacuum level (200 and 400 mbar) and vacuum application period (2 and 5 min) were evaluated. Results showed that vacuum impregnation (VI) with lactic acid solution increased the acidification degree to a greater extent than processing carried out at atmospheric pressure. In particular, samples treated at 400 and 200 mbar and submitted to a relaxation period of 30 min, showed a reduction in pH ratio (RpH) from 0.929 to 0.894. Otherwise, samples submitted to conventional dipping at atmospheric pressure showed a RpH of 0.968. Vacuum level was found to be the most important variable influencing the variations in total mass and pH. Vacuum impregnation led to an increase in diffusion rate of hydrogen ions into the vegetable tissue due to the increase in contact area between acid solution and cells. Moreover, a direct correlation between pH reduction on the one hand, and vacuum application period and relaxation time on the other, was observed. Results proved that vacuum impregnation process is a useful technique to improve acidification treatments of vegetables.     

Optimization of Vacuum Impregnation with Calcium Lactate of Minimally Processed Melon and Shelf‐Life Study in Real Storage Conditions

Vacuum impregnation (VI) is a processing operation that permits the impregnation of fruit and vegetable porous tissues with a fast and more homogeneous penetration of active compounds compared to the classical diffusion processes. The objective of this research was to investigate the impact on VI treatment with the addition of calcium lactate on qualitative parameters of minimally processed melon during storage. For this aim, this work was divided in 2 parts. Initially, the optimization of process parameters was carried out in order to choose the optimal VI conditions for improving texture characteristics of minimally processed melon that were then used to impregnate melons for a shelf‐life study in real storage conditions. On the basis of a 2³ factorial design, the effect of Calcium lactate (CaLac) concentration between 0% and 5% and of minimum pressure (P) between 20 and 60 MPa were evaluated on color and texture. Processing parameters corresponding to 5% CaLac concentration and 60 MPa of minimum pressure were chosen for the storage study, during which the modifications of main qualitative parameters were evaluated. Despite of the high variability of the raw material, results showed that VI allowed a better maintenance of texture during storage. Nevertheless, other quality traits were negatively affected by the application of vacuum. Impregnated products showed a darker and more translucent appearance on the account of the alteration of the structural properties. Moreover microbial shelf‐life was reduced to 4 d compared to the 7 obtained for control and dipped samples.     

Effect of high pressure processing on yield,quality and storage stability of peanut paneer

Paneer was prepared from peanuts by soaking the nuts for 8 h followed by removal of skin, grinding, extraction of milk and coagulation using calcium sulphate (1% solution). In another method the peanut milk was high pressure processed at 600 MPa for 5 min before coagulation. The obtained paneer samples were vacuum packed and kept at refrigerated temperature (6 ± 1 °C) for storage and evaluated for physico‐chemical, sensory and microbial attributes. High pressure processing of milk before coagulation resulted in increase in paneer yield significantly (P < 0.05) as well as maintained the quality of the paneer to a better extent as compared to control during refrigerated storage for a period of 45 days.     

Chitosan nanoparticle coatings reduce microbial growth on fresh‐cut apples while not affecting quality attributes

This study addressed the effects of chitosan‐based nanoparticles on microbiological quality, colour, polyphenol oxidase (PPO) and peroxidase (POD) and firmness of fresh‐cut ‘Gala’ apple slices during storage at 5 °C for 10 days. The treatments carried out were as follows: (i) slices pulverised with 110‐nm chitosan nanoparticles, (ii) slices pulverised with 300‐nm chitosan nanoparticles, (iii) 2 g L^?1 chitosan dissolved in 2% citric acid and (iv) noncoated samples. There was an increase in chroma and a proportional decrease in hue angle and lightness. Browning of the slices coated with conventional chitosan and control was slightly intense than those coated with chitosan nanoparticles of 110 and 300 nm. The PPO and PDO activities increased with time for all samples, with irrelevant difference among the treatments. Flesh firmness did not change for any treatment and period. Coatings with chitosan nanoparticles of 110 nm showed higher antimicrobial activity against moulds and yeasts, and mesophilic and psychrotrophic bacteria than the other treatments. No Salmonella, and total and faecal coliforms were detected. This investigation supports the potential use of chitosan nanoparticles as edible coatings in controlling microbial activity in fresh‐cut apples.     

Synergistic Effect of Sodium Chlorite and Edible Coating on Quality Maintenance of Minimally Processed Citrus grandis under Passive and Active MAP

Edible coating has been an innovation within the bioactive packaging concept. The comparative analysis upon the effect of edible coating, sodium chlorite (SC) and their combined application on quality maintenance of minimally processed pomelo (Citrus grandis) fruits during storage at 4 °C was conducted. Results showed that the combination of edible coating and SC dipping delayed the microbial development whereas the sole coating or dipping treatment was less efficient. The synergetic application of edible coating and SC treatment under modified atmosphere packaging (MAP, 10% O₂, 10% CO₂) was able to maintain the total soluble solids level and ascorbic acid content, while reduce the weight loss as well as development of mesophiles and psychrotrophs. Nonetheless, the N, O‐carboxymethyl chitosan solely coated samples showed significantly higher level of weight loss during storage with comparison to the untreated sample. Furthermore, the combined application of edible coating and SC dipping under active MAP best maintained the sensory quality of minimally processed pomelo fruit during storage.     

Effectiveness of chitosan edible coatings to improve microbiological and sensory quality of fresh cut broccoli

The effects of chitosan edible coating on microbiological and sensory quality of refrigerated broccoli were studied. The antimicrobial effects of chitosan on the native microflora (mesophilic, psychrotrophic, yeast and molds, lactic acid bacteria and coliforms) and on the survival of E. coli O157:H7 inoculated in broccoli were evaluated.Chitosan treatments resulted in a significant reduction in total mesophilic and psychrotrophic bacteria counts with respect to the control samples during the entire storage period. There was an immediate decontaminating activity of chitosan. At the end of the storage, yeast and molds was the most dominant flora representing the largest part of the total aerobic counts. Lactic acid bacteria (LAB) numbers remained relatively low during the whole storage in all samples. Chitosan coating inhibited the growth of total coliform throughout the storage time. Also, chitosan treatments resulted in a bactericidal effect on E. coli endogenous and a significant decreased in total E. coli counts (endogenous and O157:H7). The application of chitosan coating on fresh cut broccoli inhibited the yellowing and opening florets. The results of this experiment showed that the use of chitosan coating is a viable alternative in controlling the microorganisms present in minimally processed broccoli, improving its sensory quality.     

Chitosan/whey protein film as active coating to extend Ricotta cheese shelf-life

Shelf-life extension of Ricotta cheese coated with a chitosan/whey protein edible film and stored under modified atmosphere at 4 °C was evaluated. The chitosan/whey protein film had 35% and 21% lower oxygen and carbon dioxide permeability, respectively, and about three times higher water vapor permeability than film prepared with chitosan alone. Over a 30-day storage period, no differences in the pH of control and coated Ricotta cheeses were observed. While the titratable acidity of the control increased linearly during the first two weeks and remained constant for the rest of the storage period, the corresponding values for coated Ricotta cheese did not change significantly during the first 21 days and reached the acidity level (0.34 ± 0.02 milliequivalent/100 g of analyzed sample) of the control only on day 30. The viable numbers of lactic acid bacteria and mesophilic and psychrotrophic microorganisms were significantly lower (p < 0.05) in the chitosan/whey protein coated cheese, compared to the control, at each storage time. Our findings suggest a potential utility of chitosan/whey protein coatings to extend fresh dairy product shelf-life.     

Quality differences of hamburger patties incorporated with encapsulated β carotene both as an additive and edible coating

In this study, different formulations of chitosan (CS) and chitosan/sodium tripolyphosphate (CS/TPP) matrix solutions including β carotene were used as additives and edible coatings in hamburger patties, and the treatments were compared to control in terms of quality, oxidative and microbiological features of the patties. TBARS (2‐thiobarbituric acid reactive substances) values of almost all the treatments increased throughout storage at 4 °C for 8 days. (p < .05). On the last day of storage, the treatment including 5% CS/TPP with β carotene and all the coated treatments had lower TBARS values than the other treatments (p < .05). The comparison of different treatments including the solutions of chitosan or chitosan/TPP matrix containing β carotene showed that incorporation of solution as an edible coating was more effective in lipid oxidation and microbial growth than its utilization as an additive on quality of patties according to the results on last day of storage.

Practical applications

Using polymers loaded with antioxidant agents as additives or edible coatings in food products is one of the most popular scientific approaches in recent studies. In this study, hamburger patties were incorporated with chitosan/sodium tripolyphosphate (CS/TPP) matrix solution loaded with β carotene, CS/TPP matrix solution, pure chitosan solution and pure β carotene as additives and/or edible coatings. By this way, synergistic effects of β carotene with different formulations of chitosan (CS) and CS/TPP were also tested. The results showed that lipid oxidation and microbial growth in the coated patties were mostly lower than that of the other patties formulated with different additives on the last day of storage.     

Vacuum impregnation modulates the metabolic activity of spinach leaves

In this study calorimetric measurements provided evidence of a drastic increase of spinach leaf gross metabolism as a consequence of vacuum impregnation (VI) at a minimum pressure of 150 mbar with trehalose and sucrose isotonic solutions. When applying VI extracellular air is replaced by the impregnation solution, potentially limiting tissue respiration to any remaining air volume in the tissue. However the observation that impregnated leaves showed photosynthetic activity suggests that not all air was exhausted during VI. Hence impregnation appears to reach a maximum with remaining gas filled compartments. Metabolic inhibitors impregnated together with sugars showed that the short-term metabolic response, causing the drastic increase of gross metabolism upon VI, depends on mitochondrial oxygen consuming pathways. The metabolic effect following mannitol impregnation was comparable with water impregnation, suggesting that the strong metabolic effect reported here is only seen for molecules that can be metabolized and provide energy to the cells.Industrial relevanceVacuum impregnation is used to incorporate additives in fruit and vegetable tissues, such as anti-browning agents, microbial preservatives or cryoprotectants. As a promising technology in the food industry, deeper insights on the metabolic consequences of vacuum impregnation are required to define and control the shelf-life of the processed fruits and vegetables.     

The nutraceutical quality of tomato fruit during domestic storage is affected by chitosan coating

Fruits and vegetables are highly perishable foods which usually undergo a gradual loss of nutraceuticals during storage. Chitosan‐based edible coatings are extensively studied thanks to antimicrobial activity and great potential to extend the shelf life. However, little information is presently available on the nutraceutical quality of chitosan‐coated products. The present study is addressed to evaluate accompanied by a delayed degradation of some phenolic compounds during storage. These results indicate that chitosan coating is effective in maintaining the quality parameters, the coated fruit showed less weight loss (?16%) and more firmer (+40%) than control fruit, chitosan‐coated tomato emitted significantly lower ethylene (?41%) than control, and slowing down the nutraceutical loss occurring in postharvest, mainly of the lycopene, main carotenoid, found in tomato fruits. These results indicate that chitosan coating is effective in slowing down the nutraceutical loss occurring in postharvest, thus representing a promising tool to preserve bio‐protective phytochemicals during fruit conservation.

Practical applications

During storage and domestic conservation, the nutraceutical quality of fruits and vegetables usually decreases and can undergo deterioration due to physiological disorders and mechanical damages. In the last decade, use of edible coatings has attracted interest as a promising technology to prolong the shelf life of particularly perishable foods. These coatings act as protective barriers decreasing transpiration rate and gas transfer across the product surface, thus promoting the maintenance of nutritional quality.     

Control of Listeria monocytogenes on cold-smoked salmon using chitosan-based antimicrobial coatings and films

The relatively high incidence of Listeria monocytogenes in ready-to-eat (RTE) products such as cold-smoked salmon is of serious concern. The objective of this study was to evaluate the efficacy of chitosan-based edible coatings and films incorporating 3 generally recognized as safe (GRAS) antimicrobials, sodium lactate (SL), sodium diacetate (SD), and potassium sorbate (PS), against L. monocytogenes on cold-smoked salmon. Salmon samples were surface-inoculated with a 5-strain cocktail of Listeria monocytogenes to a final concentration of 4.4 log CFU/cm(2) and then either coated with chitosan solutions or wrapped with chitosan films with or without the 3 antimicrobials. The samples were then vacuum packaged and stored at 4 °C for 30 d. The chitosan coatings with or without the antimicrobials consistently showed higher efficacy against L. monocytogenes than chitosan films having the same compositions. The most effective film treatments, chitosan films containing 1.2% SL/0.25% SD or 2.4% SL, achieved ≥ 1.3 log reductions of L. monocytogenes during the 30 d of refrigerated storage, while the most effective coating treatments, chitosan coatings containing 1.2% SL/0.25% SD or 0.15% PS/0.125% SD, achieved ≥ 2.8 log reductions. Practical Application: This study shows that chitosan-based edible coatings and films hold promise and can potentially assist fishery industries in their efforts to control L. monocytogenes.     

In vivo and in vitro antifungal effect of fungal chitosan nanocomposite edible coating against strawberry phytopathogenic fungi

This study compared the effectiveness of fungal chitosan nanocomposite, chitosan gel and chitosan nanoparticles against strawberry phytopathogenic fungi (Botrytis cinerea; Rhizopus stolonifer and Aspergillus niger). Nanoparticles were prepared by ionic gelation method and characterised by dynamic light scattering and scanning electron microscopy. The influence of the edible coatings on fungal growth was analysed in vitro and in vivo The fungal chitosan nanoparticles presented an average size = 331.1 nm (±7.21) with a narrow size distribution (PDI = 0.377) and a zeta potential = +34 mV. The edible coating made by the nanocomposite exhibited important changes in fungal morphology, and the best control of the growth of the assayed fungal strains in artificially infected strawberries. Therefore, nanotechnology brought some benefits to the conventional chitosan gel edible coating, improving its antifungal activity and forming a new eco-friendly coating.     

Impregnation Techniques for Aroma Enrichment of Apple Sticks: A Preliminary Study

The food industry often utilizes flavor-enriched, semifinished food products as ingredients in more complex preparations. To the best of our knowledge, there are no methods to produce minimally processed food items to which flavorings have been added. In this investigation, apple sticks were enriched with a green apple aroma using different techniques. In particular, vacuum impregnation (VI), ultrasound technology (USI), and the combination of these two techniques (VUSI) were compared with atmospheric pressure impregnation (AI). An isotonic solution of fructose containing ascorbic acid and green apple flavoring was used for impregnation of apple sticks. Different treatment times (2.5, 5.0, and 12.5 min) were investigated, and the relative amount of the major compounds of impregnation flavoring was recorded. Significant differences between treatments were detected: VI and VUSI gave the highest aroma enrichment at 5.0 min of treatment. Different impregnation behaviors were recorded for alcohols and esters: the former increased even after 5.0 min of treatment, and the other components increased until 5.0 min and then decreased, mainly when ultrasound was applied (USI and VUSI). Some possible explanations of these results are proposed, although additional studies are needed to explain the mechanisms involved.     

Stability of quercetin derivatives in vacuum impregnated apple slices after drying (microwave vacuum drying,air drying,freeze drying) and storage

Microwave vacuum drying (MVD) was investigated for apple slices enriched with quercetin derivatives by vacuum impregnation (VI). Additional freeze drying (FD) and air drying (AD) were conducted. Compared to native apples, the impregnated tissue resulted in higher moisture content, elevation of weight and significant browning, due to the incorporated VI solution. The total quercetin content and quercetin glycoside composition were not affected by MVD and FD. The vacuum conditions protect the polyphenols from oxygen dependent degradation and browning reactions. AD resulted in an average quercetin glycoside loss of 44% and undesirable changes, particularly discoloration. The degradation is caused by both non-enzymatic and enzymatic reactions. The pulsed microwave energy intake improved the drying result in structure and led to a faster drying process of 130 min. The bulk density of MVD apple chips (0.69 g/ml) ranged between 0.33 g/ml for FD and 0.75 g/ml for AD. The final moisture content was the lowest after FD (6.8 g/100 g), followed by 9.0 g/100 g after MVD and 12.7 g/100 g after AD. The shelf life was significantly influenced by storage temperature and time. After 12 month at 20 °C, the total quercetin content decreased by 21%.