High-power ultrasound as pre-treatment in different stages of soymilk manufacturing process to increase the isoflavone content.

Ultrasound (US) was applied as a pre-treatment in hydrated soybeans (HSB) and soybean slurry (SBS) during soymilk elaboration process to evaluate the feasibility of increasing the isoflavone content (IC) in the resultant soymilk. A predictive model and optimum US processing conditions were obtained by response surface methodology (RSM) using a three-level-three-factor Box-Behnken statistical design (BBD) in which US amplitude (50, 75, and 100%), temperature (30, 45, and 60 °C), and time (20, 40, and 60 min) were selected as independent variables. Most of the US treatments applied in the HSB or SBS caused a significant increase (3-62%) in the total IC of the obtained soymilks over the control soymilk (6.97 mg/100 mL). However, the IC of the resultant soymilks from sonicated HSB (11.38 mg/100 mL) was significantly higher than that in soymilk prepared from US-treated SBS (8.66 mg/100 mL). Experimental data were fitted into a 2nd-order-polynomial model and processing parameters were optimized (100% amplitude, 30 °C, 20 min) to get the highest predicted and experimental IC, 11.38 and 12.8 mg/100 mL, respectively. These results indicated that US is a potential technology that could be implemented during soymilk manufacturing processing as pre-treatment of HSB to obtain soymilk with high isoflavone content and consequently better functionality.

Characterization of carotenoid profile of Spanish Sanguinos and Verdal prickly pear (Opuntia ficus-indica, spp.) tissues.

Carotenoid profiles of different tissues (peel, pulp and whole fruit) of Spanish Sanguinos (red) and Verdal (orange) prickly pears (Opuntia ficus-indica spp.) have been characterized in detail and quantified for the first time. Carotenoids were determined by HPLC-PDA-MS (APCI+), using a reverse phase C30 column. A total of 9 xantophylls and 4 hydrocarbon carotenes were identified. Also, minor amounts of chlorophyll a, a' and b can be observed in Opuntia peel extracts. All carotenoids were found to be present in their free form (no carotenoid esters were detected). The RAE was highest in Opuntia peels, showing values from 19.20 to 16.48µg/100g fresh weigth, for Sanguinos and Verdal Opuntia fruits, respectively. The main carotenoid in Opuntia peel extracts was (all-E)-lutein with 1132.51 and 767.98µg/100g fresh weigth, followed by (all-E)-ß-carotene with 200.40 and 173.50µg/100g fresh weigth for Sanguinos and Verdal varieties of Opuntia fruits, respectively.

Hurdle technology applied to prickly pear beverages for inhibiting Saccharomyces cerevisiae and Escherichia coli.

The effect of pH reduction (from 6·30-6·45 to 4·22-4·46) and the addition of antimicrobial compounds (sodium benzoate and potassium sorbate) on the inhibition of Saccharomyces cerevisiae and Escherichia coli in prickly pear beverages formulated with the pulp and peel of Villanueva (V, Opuntia albicarpa) and Rojo Vigor (RV, Opuntia ficus-indica) varieties during 14 days of storage at 25°C, was evaluated. RV variety presented the highest microbial inhibition. By combining pH reduction and preservatives, reductions of 6·2-log10 and 2·3-log10 for E. coli and S. cerevisiae were achieved respectively. Due to the low reduction of S. cerevisiae, pulsed electric fields (PEF) (11-15 µs/25-50 Hz/27-36 kV cm(-1)) was applied as another preservation factor. The combination of preservatives, pH reduction and PEF at 13-15 µs/25-50 Hz for V variety, and 11 µs/50 Hz, 13-15 µs/25-50 Hz for RV, had a synergistic effect on S. cerevisiae inhibition, achieving at least 3·4-log10 of microbial reduction immediately after processing, and more than 5-log10 at fourth day of storage at 25°C maintained this reduction during 21 days of storage (P > 0·05). Hurdle technology using PEF in combination with other factors is adequate to maintain stable prickly pear beverages during 21 days/25°C. Significance and impact of the study: Prickly pear is a fruit with functional value, with high content of nutraceuticals and antioxidant activity. Functional beverages formulated with the pulp and peel of this fruit represent an alternative for its consumption. Escherichia coli and Saccharomyces cerevisiae are micro-organisms that typically affect fruit beverage quality and safety. The food industry is looking for processing technologies that maintain quality without compromising safety. Hurdle technology, including pulsed electric fields (PEF) could be an option to achieve this. The combination of PEF, pH reduction and preservatives is an alternative to obtain safe and minimally processed prickly pear beverages with convenient shelf-life.

Multiple-pass high-pressure homogenization of milk for the development of pasteurization-like processing conditions.

Multiple-pass ultrahigh pressure homogenization (UHPH) was used for reducing microbial population of both indigenous spoilage microflora in whole raw milk and a baroresistant pathogen (Staphylococcus aureus) inoculated in whole sterile milk to define pasteurization-like processing conditions. Response surface methodology was followed and multiple response optimization of UHPH operating pressure (OP) (100, 175, 250 MPa) and number of passes (N) (1-5) was conducted through overlaid contour plot analysis. Increasing OP and N had a significant effect (P < 0·05) on microbial reduction of both spoilage microflora and Staph. aureus in milk. Optimized UHPH processes (five 202-MPa passes; four 232-MPa passes) defined a region where a 5-log(10) reduction of total bacterial count of milk and a baroresistant pathogen are attainable, as a requisite parameter for establishing an alternative method of pasteurization. Multiple-pass UHPH optimized conditions might help in producing safe milk without the detrimental effects associated with thermal pasteurization.

Formation risk of toxic and other unwanted compounds in pressure-assisted thermally processed foods.

Consumers demand, in addition to excellent eating quality, high standards of microbial and chemical safety in shelf-stable foods. This requires improving conventional processing technologies and developing new alternatives such as pressure-assisted thermal processing (PATP). Studies in PATP foods on the kinetics of chemical reactions at temperatures (approximately 100 to 120 °C) inactivating bacterial spores in low-acid foods are severely lacking. This review focuses on a specific chemical safety risk in PATP foods: models predicting if the activation volume value (V(a) ) of a chemical reaction is positive or negative, and indicating if the reaction rate constant will decrease or increase with pressure, respectively, are not available. Therefore, the pressure effect on reactions producing toxic compounds must be determined experimentally. A recent model solution study showed that acrylamide formation, a potential risk in PATP foods, is actually inhibited by pressure (that is, its V(a) value must be positive). This favorable finding was not predictable and still needs to be confirmed in food systems. Similar studies are required for other reactions producing toxic compounds including polycyclic aromatic hydrocarbons, heterocyclic amines, N-nitroso compounds, and hormone like-peptides. Studies on PATP inactivation of prions, and screening methods to detect the presence of other toxicity risks of PATP foods, are also reviewed.

Study of the inactivation of Escherichia coli and pectin methylesterase in mango nectar under selected high hydrostatic pressure treatments.

High hydrostatic pressure (HHP) was applied to fresh mango nectar (FMN) and sterilized mango nectar (SMN) to inactivate Escherichia coli and pectin methylesterase (PME). Pressure was applied at 275, 345 and 414 MPa. The come-up time (CUT) as well as 1, 2 and 4 min of treatment times were applied at the selected pressure to evaluate the inactivation effect on E. coli and PME. Total plate counts (TPC) were also evaluated in FMN. Results showed that mesophiles are inactivated in FMN to an important degree (up to 4 log) only with the CUT; the highest inactivation for mesophiles (7 log) was reported at 414 MPa after 4 min. Meanwhile, for E. coli 345 and 414 MPa after 2 and 1 min, respectively, were able to inactivate all viable cells in FMN. However, in SMN after 4 min at 275 MPa all cells of E. coli were also inactivated, showing the protective effect of the media between FMN and SMN. The PME showed its resistance to be inactivated with high pressure, showing the highest decrease in enzymatic activity (45%) after 4 min at 345 MPa but with an important activation at the highest pressure (414 MPa).

Oscillatory high hydrostatic pressure inactivation of Zygosaccharomyces bailii.

Zygosaccharomyces bailii inactivation was evaluated in oscillatory high hydrostatic pressure (HHP) treatments at sublethal pressures (207, 241, or 276 MPa) and compared with continuous HHP treatments in laboratory model systems with a water activity (aw) of 0.98 and pH 3.5. The yeast was inoculated into laboratory model systems and subjected to HHP in sterile bags. Two HHP treatments were conducted: continuous (holding times of 5, 10, 15, 20, 30, 60, or 90 min) and oscillatory (two, three, or four cycles with holding times of 5 min and two cycles with holding times of 10 min). Oscillatory pressure treatments increased the effectiveness of HHP processing. For equal holding times, Z. bailii counts decreased as the number of cycles increased. Holding times of 20 min in HHP oscillatory treatments at 276 MPa assured inactivation (< 10 CFU/ml) of Z. bailii initial inoculum. Oscillatory pressurization could be useful to decrease Z. bailii inactivation time.

High hydrostatic pressure come-up time and yeast viability.

The effects of the come-up time at selected pressures (50 to 689 MPa) on Saccharomyces cerevisiae and Zygosaccharomyces bailii viability were evaluated at 21 degrees C. For Z. bailii the effects of the water activity (a(w)) of the suspension media and the stage of the growth cycle were also investigated. Pressure come-up times exerted an important effect on the yeast survival fraction, decreasing counts as pressure increased. An increased sensitivity to pressure treatments was observed with yeast cells from the exponential growth phase. Lethality increased as a(w) of the suspension media increased. For an a(w) of 0.98 and cells from the stationary growth phase, pressure treatments at less than 200 MPa had no effect on Z. bailii viability; however, no survivors (< 10 CFU/ml) were observed in treatments applied only for the time needed to reach pressures greater than 517 MPa. Yeast survivor curves showed an excellent fit (r > 0.996) when described by a phenomenological model based on the Fermi equation, S(P) = 1/¿1 + exp[(P - Pc)/k]¿, where S(P) is the survival fraction, P is the pressure, Pc is a critical pressure corresponding to 50% survival, and k is a constant representing the steepness of the curve.

Effect of oscillatory high hydrostatic pressure treatments on Byssochlamys nivea ascospores suspended in fruit juice concentrates.

The effect of continuous (689 MPa with holding times of 5, 15 or 25 min) and oscillatory (one, three or five cycles at 689 MPa with holding times of 1 s) high hydrostatic pressure treatments on the viability of Byssochlamys nivea ascospores suspended in apple and cranberry juice concentrates adjusted by dilution to water activities (aw) of 0.98 and 0.94 was evaluated at 21 and 60 degrees C. Inactivation of the initial spore inocula was achieved after three or five cycles of oscillatory pressurization at 60 degrees C when the aw was 0.98 in both fruit juices. With aw 0.94, the initial inocula were reduced by less than 1 log-cycle after five pressure cycles. Inactivation was not observed within 25 min with continuous pressurization at 60 degrees C. In treatments at 21 degrees C, no effect on spore viability was observed with continuous or oscillatory treatments.