Effect of high hydrostatic pressure pretreatment on drying kinetics, antioxidant activity, firmness and microstructure of Aloe vera (Aloe barbadensis Miller) gel

The effect of High Hydrostatic Pressure (HHP) and other pretreatments on the drying kinetics, antioxidant activity, firmness and microstructure of Aloe vera gel was investigated during convective drying at 70 °C. The pretreatments analyzed were high hydrostatic pressure, blanching, enzymatic and microwaves. Simulation of drying curves was studied through the application of several mathematical models such as Newton, Henderson and Pabis, Page, Modified Page, Wang and Singh, and Weibull. Among them, the Weibull model provided the best fit for the experimental data. All pretreatments increased the water diffusion coefficient compared to the control sample. Microwaves followed by HHP presented the fastest drying rates. All pretreatments modified the microstructure and hence the texture of the product. HHP and microwaves increased firmness while blanching and enzymatic treatments produced a softer final product. Blanching, microwaves and HHP enhanced A. vera antioxidant activity. However, the HHP pretreated samples showed the highest antioxidant activity compared to the rest. Based on these results, HHP together with convective drying offers the chance of producing dried aloe with high antioxidant attributes.     

Modeling mass transfer during osmotic dehydration of strawberries under high hydrostatic pressure conditions

Simultaneous application of high hydrostatic pressure (200–400 MPa) during osmotic dehydration of strawberries was studied in this investigation. The high hydrostatic pressure treatment improved the diffusion coefficients of water and soluble solids compared to atmospheric pressure operation. Effects of process pressure on diffusion coefficients were achieved through an Arrhenius-type equation. Mathematical modeling of mass transfer was performed applying Newton, Henderson–Pabis, Page and Weibull models. Based on statistical results, the Weibull model gave the best goodness of fit on the experimental data under the studies' operative conditions.Industrial relevance: This article deals with the mathematical modeling of mass transfer during simultaneous high hydrostatic pressure treatment and osmotic dehydration of strawberries. Transfer of water and soluble solids during this combined process were satisfactorily simulated with the Weibull model. Results indicated that application of this innovative technology improved strawberries dehydration rates compared to atmospheric pressure operation resulting in a dried fruit with intermediate moisture content ready to be used as input material of further processes.     

Influence of temperature,calcium and sucrose concentration on viscoelastic properties of Prosopis chilensis seed gum and nopal mucilage dispersions

Viscoelastic properties of two nontraditional hydrocolloid dispersions were evaluated. Prosopis chilensis seed gum was evaluated based on temperature (5–80 °C) and added CaCl₂ (0.07%), whereas nopal mucilage was evaluated based on temperature (5–80 °C) and sucrose concentration (0–20%). Viscoelasticity was tested by the small strain oscillatory shear test; storage modulus (G′), loss modulus (G″) and tan δ were reported. Prosopis chilensis and nopal dispersions behaved as weak gels (G’ > G’’) regardless of experimental condition. Raising temperature from 20 to 80 °C significantly increased G’. The gel structure was strengthened by adding CaCl₂ and G’ increased at 40 °C. The sucrose effect depended on concentration and temperature; at low sucrose concentrations, G’ modulus increased regardless of temperature level, but at high concentrations, it decreased at temperatures >40 °C. In conclusion, nopal and Prosopis chilensis dispersions show weak gel structure regardless of experimental condition. G′ increases as temperature increases, and these dispersions could be suitable for food applications requiring heat tolerance.     

Effect of high hydrostatic pressure on functional properties and quality characteristics of Aloe vera gel (Aloe barbadensis Miller)

The aim of this study was to evaluate the effects of high hydrostatic pressure treatment at three pressure levels (300, 400 and 500 Mpa) on the functional and quality characteristics of Aloe vera gel including vitamin C and E, aloin, minerals, phenolic content and antioxidant activity. The results show that HHP exerted a clear influence on minerals content, vitamin C and E content, antioxidant activity, total phenolic and aloin content. After 35 days of storage all treated samples presented a decrease in mineral content, except for phosphorus. Total phenolic content and vitamin C and E content decreased at high pressures (500 MPa), while all pressurised samples showed a higher antioxidant activity and aloin content than untreated sample after 35 days of storage. The maximum values of antioxidant activity and aloin were 6.55 ± 1.26 μg/ml at 300 MPa and 24.23 ± 2.27 mg/100 g d.m. at 400 MPa.     

Headspace components that discriminate between thermal and high pressure high temperature treated green vegetables: Identification and linkage to possible process-induced chemical changes

For the first time in literature, this study compares the process-induced chemical reactions in three industrially relevant green vegetables: broccoli, green pepper and spinach treated with thermal and high pressure high temperature (HPHT) processing. Aiming for a fair comparison, the processing conditions were selected based on the principle of equivalence. A comprehensive integration of MS-based metabolic fingerprinting techniques, advanced data preprocessing and statistical data analysis has been implemented as untargeted/unbiased multiresponse screening tool to uncover changes in the volatile fraction. For all vegetables, thermal processing, compared to HPHT, seems to enhance Maillard and Strecker degradation reaction, triggering the formation of furanic compounds and Strecker aldehydes. In most cases, high pressure seems to accelerate (an)aerobic thermal degradation of unsaturated fatty acids leading to the formation of aliphatic aldehydes and ketones. In addition, both thermal and HPHT processing accelerated the formation of sulfur-containing compounds. This work demonstrated that the approach is effective in identifying and comparing different process-induced chemical changes, adding depth to our perspective in terms of studying a highly complex chemical changes occurring during food processing.     

Inhibition of lipid damage in refrigerated salmon (Oncorhynchus kisutch) by a combined treatment of CO2 packaging and high-pressure processing

The effect of a previous combined treatment (CO₂-enriched modified atmosphere packaging, MAP and high-pressure processing, HPP, 150 MPa/5 min) on lipid stability of refrigerated (10 days/4 °C) salmon (Oncorhynchus kisutch) was studied. The following processing conditions were compared: B-0 (fish without MAP or HPP), B-1 (fish packaged under MAP and without HPP), B-2 (fish subjected to HPP without MAP) and B-3 (fish subjected to MAP and HPP). An inhibitory effect (P < 0.05) on lipid hydrolysis and oxidation was obtained by the presence of CO₂ in the packaging medium; values detected at day 10 for B-0 and B-1 fish were 80.72 and 49.61 (g free fatty acids, FFA, kg⁻¹ lipids), 6.14 and 2.81 (meq active oxygen kg⁻¹ lipids; peroxide value), 5.05 and 3.10 (mg malondialdehyde kg⁻¹ muscle), and 5.56 and 2.70 (fluorescence ratio), respectively. Furthermore, inhibition of lipid damage was observed for HPP alone; values detected at day 10 for B-2 fish were 76.24 (g FFA kg⁻¹ lipids) and 5.28 (meq active oxygen kg⁻¹ lipids). The lowest average values for lipid hydrolysis and oxidation were obtained in samples corresponding to the combined treatment (B-3 batch), differences being significant (P < 0.05) at day 10 for FFA (41.43 g kg⁻¹ lipids), peroxide (1.84 meq kg⁻¹ lipids) and fluorescence (2.50) values.     

Microbiological stabilization of Aloe vera (Aloe barbadensis Miller) gel by high hydrostatic pressure treatment

The effect of high hydrostatic pressure (HHP) treatment (300, 400 and 500MPa for 1 and 3min at 20°C) on the microbiological shelf-life and microbiota composition of Aloe vera gel during 90days of storage at 4°C was investigated. Aerobic mesophilic and psychrotrophic bacteria, as well as moulds and yeasts, were enumerated after HHP treatment and through cold storage. Randomly selected isolates from the count plates were identified by standard methods and the API identification system. Results showed that HHP treatment at or over 400MPa for 3min were effective to keep the microbial counts to undetectable levels during the whole storage period, and consequently the microbiological shelf-life of A. vera gel was extended for more than 90days at 4°C. The microbiota in the untreated A. vera gel was dominated by Gram-negative bacteria (mostly Rahnella aquatilis) and yeasts (mostly Rhodotorula mucilaginosa). In contrast, Gram-positive bacteria tentatively identified as Arthrobacter spp. and Micrococcus/Kocuria spp. were the predominant microorganisms in samples pressurized at 300MPa for 1 and 3min, while Bacillus megaterium predominating in samples treated at 400MPa for 1min. At 400MPa for 3min and above, the microbial growth was completely suppressed during at least 90days; however, viable spore-formers were detected by enrichment.     

Sensory and Physical Changes in Chilled Farmed Coho Salmon (Oncorhynchus kisutch): Effect of Previous Optimized Hydrostatic High-Pressure Conditions

The effect of a previous hydrostatic high-pressure (HHP) treatment on sensory and physical quality of chilled coho salmon (Oncorhynchus kisutch) was investigated. As a first stage, a 2² factorial design based on the response surface methodology was used for optimization of HHP conditions; for it, the effects on color uniformity, white spots appearance, elasticity, and hardness were analyzed. In a second stage, optimized HHP conditions (135 MPa for 30 s, 170 MPa for 30 s, and 200 MPa for 30 s; treatments T-1, T-2, and T-3, respectively) were applied as previous treatment to chilling, being sampling carried out on salmon muscle at days 0, 6, 10, 15, and 20. A marked effect on sensory and physical parameters was detected after HHP treatment and throughout the chilled storage. According to odor (rancid, putrid), texture (elasticity, gaping, firmness), and color (L* value) attributes, fish corresponding to T-1 condition was shown to have better-maintained quality throughout the chilled storage than fish belonging to T-2 and T-3 conditions; additionally, a quality enhancement (putrid odor, cohesivity, gaping) was found when compared with control samples. In agreement to the preliminary optimization study, it is concluded that T-1 condition can provide the most effective HHP pre-treatment to better maintain sensory and physical properties when salmon muscle is to be commercialized as a fresh product. Results obtained for the quality evolution of chilled fish attest the importance of establishing a judicious selection of previous HHP treatment parameters to minimize undesirable changes related to sensory and physical characteristics.     

Effect of high‐pressure treatment on microbial activity and lipid oxidation in chilled coho salmon

This work studies the effect of a previous hydrostatic high‐pressure (HHP) treatment on chilled farmed coho salmon (Oncorhynchus kisutch). Three different HHP conditions were applied (135 MPa‐30 s, 170 MPa‐30 s, and 200 MPa‐30 s for treatments T‐1, T‐2, and T‐3, respectively) and compared to untreated (control) fish throughout a 20‐day chilled storage. Microbial activity and lipid oxidation development were analyzed. Assessment of aerobe, psychrotroph, Shewanella spp. and Pseudomonas spp. counts and trimethylamine formation showed a marked inhibitory effect (p <0.05) of HHP treatment on microbial activity, with this effect increasing with the pressure value employed. Related to lipid oxidation development, higher peroxide mean values (day 10–20 period) were found in control samples and fish treated under T‐1 condition when compared to their counterparts corresponding to T‐2 and T‐3 treatments. On the contrary, quantification of thiobarbituric acid‐reactive substances and fluorescent interaction compounds showed higher levels (p <0.05) in fish samples corresponding to T‐2 and T‐3 treatments. In spite of the lipid oxidation development found, polyene index and tocopherol isomer (α and γ) content did not provide differences (p >0.05) as a result of previous HHP treatment.     

Effect of hydrostatic high-pressure treatment on proteins, lipids and nucleotides in chilled farmed salmon (Oncorhynchus kisutch) muscle

The effect of a previous hydrostatic high-pressure (HHP) treatment on hydrolysis, breakdown and aggregation events in chemical constituents of chilled farmed coho salmon (Oncorhynchus kisutch) was studied. Three different HHP conditions were applied (135 MPa-30 s; 170 MPa-30 s; 200 MPa-30 s; treatments T-1, T-2 and T-3, respectively) and compared to untreated fish for a 20-day chilled storage. Nucleotide degradation was important during the chilled storage in all kinds of samples; however, the K value did not afford differences related to previous pressure applied. HHP treatment led to an increased free fatty acid (FFA) formation (day 0 values); on the contrary, an inhibitory effect on FFA formation could be observed at the end of the storage (15–20 days) in T-3-treated fish as a result of microbial activity inhibition. A marked decrease in sarcoplasmic protein content was evident in samples corresponding to T-2 and T-3 treatments; the SDS–PAGE analysis of such protein fraction showed a partial loss of a band corresponding to 29 kDa. This band was excised, digested with trypsin, analysed by tandem mass spectrometry and identified as phosphoglycerate mutase.