Shelf-Life Enhancement Applying Pulsed Electric Field and High-Pressure Treatments Prior to Osmotic Dehydration of Fresh-Cut Potatoes

From a quality standpoint, it is desirable to preserve the characteristics of fresh-cut potatoes at their peak. However, due to the mechanical tissue damage during the cutting process, potatoes are susceptible to enzymatic browning. This study pertains to the selection of the appropriate osmotic dehydration (OD), high pressure (HP), and pulsed electric fields (PEF) processing conditions leading to effective quality retention of potato cuts. PEF (0.5 kV/cm, 200 pulses) or HP (400 MPa, 1 min) treatments prior to OD (35 °C, 120 min) were found to promote the retention of the overall quality (texture and color) of the samples. The incorporation of anti-browning agents (ascorbic acid and papain) into the osmotic solution improved the color retention, especially when combined with PEF or HP due to increased solid uptake (during OD) as indicated by DEI index (2.30, 1.93, and 2.10 for OD treated 120 min, non-pre-treated, HP pre-treated, and PEF pre-treated samples, respectively). PEF and HP combined with OD and anti-browning agent enrichment are sought to improve the quality and microbial stability of fresh-cut potatoes during refrigerator storage. Untreated fresh-cut potatoes were characterized by color degradation from the 2nd day of storage at 4 °C, and presented microbial growth (total viable counts: 6 log (CFU)/g) at day 6, whereas pre-treated potato samples retained their color and microbiologically stability after 6 days of cold storage (total viable counts, <4 log(CFU)/g).

Transglycosylation of Stevioside by a Commercial β-Glucanase with Fungal Extracted β-Glucans as Donors

Abstract

Alternative sweeteners, such as steviol glucosides from the plant Stevia rebaudiana Bertoni, are becoming increasingly popular for the design of next-generation foodstuffs. However, the bitter aftertaste of native steviol glucosides is one of the main reasons behind consumer reluctance towards stevia-containing products. Biocatalysis could be a sustainable solution to this problem, through addition of glucosyl moieties to the molecule. Glycoside hydrolases are enzymes performing transglycosylation reactions, and they can be exploited for such modifications. In the present work, the commercial β-glucanase Finizym 250L® was employed for the transglycosylation of stevioside. After optimization of several reaction parameters, the maximal reaction yield obtained was 19%, with barley β-glucan as the glycosyl donor. With the aim to develop a sustainable process, β-glucan extracts from different fungal sources were prepared. Pulsed Electric Field pretreatment of mycelial biomass resulted in extracts with higher β-glucan content. The extracts were tested as alternative glucosyl donors, reaching up to 15.5% conversion yield, from Pleurotus-extracted β-glucan. Overall, in the present work a novel enzymatic process for the modification of stevioside is proposed, with concomitant valorization of β-glucans extracted from fungal biomass, potentially generated as a byproduct from other applications, in concert with the principles of circular economy.

Graphical Abstract

Active and Intelligent Packaging for Enhancing Modified Atmospheres and Monitoring Quality and Shelf Life of Packed Gilthead Seabream Fillets at Isothermal and Variable Temperature Conditions

The study investigated the effect of active modified atmosphere packaging (20% CO2–60% N2–20% O2) with CO2 emitters (MAP-PAD) and conventional MAP (MAP) on the quality and shelf-life of gilthead seabream fillets during chill storage, while the most appropriate enzymatic Time Temperature Integrators (TTI) were selected for monitoring their shelf-life at isothermal and variable temperature storage conditions (Teff = 4.8 °C). The concentration of CO2 and O2 in the headspace of the package, volatile compounds and of the microbial population were monitored during storage. The kinetic parameters for bacterial growth were estimated at 0–10 °C using the Baranyi growth model. The MAP-PAD samples presented significantly lower microbial growth rates and longer lag phases compared to the MAP samples, leading to significant shelf-life extension: 2 days of extension at 2.5 °C and 5 °C, while 50% extension at variable conditions (Teff = 4.8 °C). CO2 emitters in the package improved the chemical freshness (K-values) and volatile compounds (characterizing freshness). The responses of different enzymatic TTI were modeled as the function of enzyme concentration, temperature and storage time. The activation energy (Ea) ranged from 97 to 148 kJ mol−1, allowing the selection of appropriate TTIs for the shelf-life monitoring of each fish product: LP-150U for the MAP and M-25U for the MAP-PAD samples. The validation experiment at Teff = 4.8 °C confirmed the applicability of Arrhenius-type models, as well as the use of TTIs as effective chill chain management tools during distribution and storage.

Effect of pulsed electric field treatment on the kinetics of rehydration, textural properties, and the extraction of intracellular compounds of dried chickpeas

This study investigated the effect of pulsed electric fields (PEF) pretreatment on rehydration kinetics, firmness, and release of intracellular components of dried chickpeas during rehydration at 35 to 65°C. After soaking preconditioning, chickpeas were subjected to PEF treatments (2.5 and 3.3 kV/cm, 0.2 to 12.0 kJ/kg, 15 µs pulse width, 20 Hz frequency). PEF treated and untreated chickpeas were dried in crossflow air dryer and their rehydration at constant seed/water ratio of 1:5 was studied for 24 hr. During rehydration, moisture, firmness, and concentration of released proteins, carbohydrates and raffinose family oligosaccharides (RFO) were determined and described using appropriate mathematical models. PEF treatment led to up to 70% higher rehydration rates of dried chickpeas. This increase corresponds to rehydration time of approximately 1.5 hr, as opposed to 5 hr for untreated samples. Firmness of PEF treated chickpeas (for energy inputs higher than 3 kJ/kg) during rehydration decreased up to 30% compared to untreated samples. The firmness of untreated samples after 300 min of rehydration was achieved at much shorter times (up to 30 min) for PEF treated samples. At the end of 300 min of rehydration, more than 47.7%, 76.1%, and 86.6% of total raffinose, stachyose, and verbascose, respectively has been extracted, but only 0.03% of nutritionally valuable proteins from PEF treated chickpeas. Consequently, this study demonstrates that PEF processing could be implemented in dried chickpeas processing as pretreatment, for the reduction of rehydration time prior to cooking and of intestinal discomfort caused by RFO.

A novel thermophile β-galactosidase from Thermothielavioides terrestris producing galactooligosaccharides from acid whey

β-Galactosidases are key enzymes in the food industry. Apart from the hydrolysis of the saccharide bond of lactose, they also catalyze transgalactosylation reactions, producing galactooligosaccharides (GOS) with prebiotic activity. Here we report the heterologous production in Pichia pastoris of a novel β-galactosidase from the fungus Thermothielavioides terrestris. The enzyme (TtbGal1) was purified and characterized, showing optimal activity at 60 °C and pH 4. TtbGal1 is thermostable, retaining almost full activity for 24 h at 50 °C. It was applied to the production of GOS from defined lactose solutions and acid whey, a liquid waste from the Greek yoghurt industry, reaching yields of 19.4 % and 14.8 %, respectively. HILIC-ESI-QTOF-MS analysis revealed the production of GOS with up to 4 saccharide monomers. The results demonstrate efficient GOS production catalyzed by TtbGal1, valorizing acid whey, a waste with a heavy polluting load from the dairy industry.

Effect of storage on the rheological and viscoelastic properties of mayonnaise emulsions of different oil droplet size

The rheological and viscoelastic properties of mayonnaise emulsions with different size of oil droplets were investigated. Α programmable rotational rheometer was used for the measurements and flow curves were determined at constant and variable shear rate. Mayonnaise exhibited a non-Newtonian, shear-thinning flow with yield stress and time-dependent features. The data from rotational tests were modeled by the Herschel-Bulkley equation. The temperature-dependence of η _a was modelled using the Arrhenius equation. Activation energy, E _a ranged from 15 to 20 kJ/mol. Viscoelastic properties were characterized using small amplitude oscillatory shear. Mayonnaise exhibited weak gel-like properties. The values of apparent and complex viscosity were correlated using the generalised Cox-Merz rule. According to the obtained values of parameter α, this rule could not be cut-down to one-parameter linear function. The rheological characteristics of mayonnaise were well correlated to the size of oil droplets.

Perspectives from CO+RE: How COVID-19 changed our food systems and food security paradigms

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Effect of pulsed electric fields and high pressure on improved recovery of high-added-value compounds from olive pomace

Olive pomace is considered a solid by-product and a rich source of valuable compounds such as polyphenols, flavonoids with antioxidant properties, and proteins. Nonthermal technologies, which cause alterations to cell permeability, are being explored to assist conventional recovery techniques. The aim of this study was to assess the effect of pulsed electric fields (PEF) and high pressure (HP) on improved recovery yield of the high-added-value compounds or to shorten the extraction time of these compounds. Olive pomace (Tsounati cv) was pretreated with PEF (1.0 to 6.5 kV/cm, 0.9 to 51.1 kJ/kg, and 15 µs pulse width) or HP (200 to 600 MPa and 0 to 40 min). Evaluation of the intracellular compounds extracted via solid-liquid extraction (50% ethanol-water solution) was performed. More intense PEF and HP conditions resulted in a significant increase of the phenolic concentration up to 91.6% and 71.8%, respectively. The increased antioxidant capacity of each extract was correlated to phenolic compound concentration. The protein concentration that was achieved with PEF pretreatment was doubled; however, HP-pretreated extracts reached 88.1% higher yield than untreated for pressures up to 200 MPa. HP and PEF pretreatment decreased extraction completion time t₉₈ (needed time to recover the equal amount of phenolics and proteins of untreated after 60 min of conventional extraction) to 12 min and lower than 1 min, respectively. To conclude, both pretreatments are effective in improving the conventional extraction process for increased yield recovery of high-added-value compounds from olive pomace.

Experimental data from flesh quality assessment and shelf life monitoring of high pressure processed European sea bass (Dicentrarchus labrax) fillets

Fresh fish are highly perishable food products and their short shelf-life limits their commercial exploitation and leads to waste, which has a negative impact on aquaculture sustainability. New non-thermal food processing methods, such as high pressure (HP) processing, prolong shelf-life while assuring high food quality. The effect of HP processing (600MPa, 25 °C, 5min) on European sea bass (Dicentrarchus labrax) fillet quality and shelf life was investigated. The data presented comprises microbiome and proteome profiles of control and HP-processed sea bass fillets from 1 to 67 days of isothermal storage at 2 °C. Bacterial diversity was analysed by Illumina high-throughput sequencing of the 16S rRNA gene in pooled DNAs from control or HP-processed fillets after 1, 11 or 67 days and the raw reads were deposited in the NCBI-SRA database with accession number PRJNA517618. Yeast and fungi diversity were analysed by high-throughput sequencing of the internal transcribed spacer (ITS) region for control and HP-processed fillets at the end of storage (11 or 67 days, respectively) and have the SRA accession number PRJNA517779. Quantitative label-free proteomics profiles were analysed by SWATH-MS (Sequential Windowed data independent Acquisition of the Total High-resolution-Mass Spectra) in myofibrillar or sarcoplasmic enriched protein extracts pooled for control or HP-processed fillets after 1, 11 and 67 days of storage. Proteome data was deposited in the ProteomeXchange Consortium via the PRIDE partner repository with the dataset identifiers PXD012737. These data support the findings reported in the associated manuscript “High pressure processing of European sea bass (Dicentrarchus labrax) fillets and tools for flesh quality and shelf life monitoring”, Tsironi et al., 2019, JFE 262:83–91, doi.org/10.1016/j.jfoodeng.2019.05.010.

Yoghurt-Type Gels from Skim Sheep Milk Base Enriched with Whey Protein Concentrate Hydrolysates and Processed by Heating or High Hydrostatic Pressure

An objective of the present study was the enrichment of skim sheep yoghurt milk base with hydrolysates (WPHs) of whey protein concentrate (WP80) derived from Feta cheesemaking. Moreover, the use of high hydrostatic pressure (HP) treatment at 600 MPa/55 C/10 min as an alternative for heat treatment of milk bases, was studied. In brief, lyophilized trypsin and protamex hydrolysates of WP80 produced under laboratory conditions were added in skim sheep milk. The composition and heat treatment conditions were set after the assessment of the heat stability of various mixtures; trisodium citrate was used as a chelating agent, when needed. According to the results, the conditions of heat treatment were more important for the physical properties of the gel than the type of enrichment. High pressure treatment resulted in inferior gel properties, irrespective of the type of enrichment. Supplementation of skim sheep milk with whey protein hydrolysates at >0.5% had a detrimental effect on gel properties. Finally, skim sheep milk base inoculated with fresh traditional yoghurt, resulted in yoghurt-type gels with high counts of Lb. delbrueckii subsp. bulgaricus and Str. thermophilus -close to the ideal 1:1- and with a high ACE inhibitory activity >65% that were not essentially affected by the experimental factors.

Shelf-life prediction models for ready-to-eat fresh cut salads: Testing in real cold chain

The aim of the study was to develop and test the applicability of predictive models for shelf-life estimation of ready-to-eat (RTE) fresh cut salads in realistic distribution temperature conditions in the food supply chain. A systematic kinetic study of quality loss of RTE mixed salad (lollo rosso lettuce-40%, lollo verde lettuce-45%, rocket-15%) packed under modified atmospheres (3% O2, 10% CO2, 87% N2) was conducted. Microbial population (total viable count, Pseudomonas spp., lactic acid bacteria), vitamin C, colour and texture were the measured quality parameters. Kinetic models for these indices were developed to determine the quality loss and calculate product remaining shelf-life (SLR). Storage experiments were conducted at isothermal (2.5-15°C) and non-isothermal temperature conditions (Teff=7.8°C defined as the constant temperature that results in the same quality value as the variable temperature distribution) for validation purposes. Pseudomonas dominated spoilage, followed by browning and chemical changes. The end of shelf-life correlated with a Pseudomonas spp. level of 8 log(cfu/g), and 20% loss of the initial vitamin C content. The effect of temperature on these quality parameters was expressed by the Arrhenius equation; activation energy (Ea) value was 69.1 and 122.6kJ/mol for Pseudomonas spp. growth and vitamin C loss rates, respectively. Shelf-life prediction models were also validated in real cold chain conditions (including the stages of transport to and storage at retail distribution center, transport to and display at 7 retail stores, transport to and storage in domestic refrigerators). The quality level and SLR estimated after 2-3days of domestic storage (time of consumption) ranged between 1 and 8days at 4°C and was predicted within satisfactory statistical error by the kinetic models. Teff in the cold chain ranged between 3.7 and 8.3°C. Using the validated models, SLR of RTE fresh cut salad can be estimated at any point of the cold chain if the temperature history is known. Shelf-life models of validated applicability can serve as an effective tool for shelf-life assessment and the development of new products in the fresh produce food sector.