Perla A. Gómez

Physical, Physiological and Microbial Deterioration of Minimally Fresh Processed Fruits and Vegetables

Minimally fresh processed (MFP) or fresh-cut fruits and vegetables is currently the fastest growing sub-sector of the food industry with still a high potential of growth world wide. The practical advantages and convenience they provide to consumers undoubtedly favour this fact. However, because of their specific ways of preparation, MFP plant foods are highly perishable. To minimise this, they must be elaborated following strict control procedures in order to avoid quality loss, assuring food safety to consumers. The most common physical, physiological and microbial causes of deterioration that involve the preparation of these kind of products as well as the main procedures used to avoid undesirable changes are described in this review.

Hot water, UV-C and superatmospheric oxygen packaging as hurdle techniques for maintaining overall quality of fresh-cut pomegranate arils

BACKGROUND In recent years there has been increasing consumer pressure to avoid the use of agrochemicals such as chlorine on fresh plant products for extending their shelf life. The combined use of eco-sustainable techniques may be an alternative. The effect of hot water (HW), ultraviolet-C (UV-C) light and high oxygen packaging (HO) on the overall quality of fresh-cut pomegranate arils stored under modified atmosphere packaging (MAP) for up to 14 days at 5 °C was studied. RESULTS Arils extracted manually, washed with chlorine (100 µL L⁻¹ NaClO, pH 6.5, 5 °C water), rinsed and drained were exposed to single or combined (double and triple) hurdle techniques. The HW treatment consisted of a 30 s immersion in water at 55 °C followed by air surface drying. A 4.54 kJ m⁻² dose was used for the UV-C treatment before packaging. Active MAP with initial 90 kPa O₂ was used in the HO treatment. The respiration rate remained relatively constant throughout shelf life, with no differences among treatments. CO₂ accumulation was higher within HO packages. HW induced a slight reduction in total soluble solids, while no changes in titratable acidity were found. HO-treated arils had the highest phenolic content, while the lowest was found in HW-treated arils. The lowest antioxidant activity was found in HW + UV-C + HO and the highest in UV-C + HO and HO treatments. HW alone or in combination with UV-C and HO inhibited mesophile, mould and yeast growth, while UV-C + HO was most effective for controlling yeast and mould growth. CONCLUSION UV-C and HO either alone or in combination are promising techniques to preserve the quality of pomegranate arils for up to 14 days at 5 °C.

Quality of fresh-cut baby spinach grown under a floating trays system as affected by nitrogen fertilisation and innovative packaging treatments

BACKGROUND Alternative techniques for cultivation of leafy vegetables such as a floating tray system and unconventional gas mixtures for post-harvest active modified atmosphere packaging (MAP) could be of interest in the minimally processed vegetable industry. RESULTS The combined effect of three pre-harvest fertilisation doses (8, 12 or 16 mmol N L(-1)) and three post-harvest MAP conditions (passive, super-atmospheric or N2O-enriched) on the main quality attributes of fresh-cut baby spinach leaves throughout 10 days at 5 degrees C was studied. After 8 days of shelf life, spinach leaves fertilised with 8 and 16 mmol N L(-1) and stored under N2O-enriched MAP showed the lowest microbial growth, with good sensory quality. Such combined treatments also preserved the total antioxidant capacity sampled at harvest (8 g ascorbic acid equivalent antioxidant capacity kg(-1) f.w.). A decrease of 10-20% in total vitamin C content regardless of N fertilisation and packaging treatment was found during shelf life. Total phenolics content at harvest was 2 g gallic acid equivalents kg(-1) f.w., which was slightly decreased or preserved during shelf life while total chlorophylls were preserved for all treatments assayed around 550 mg kg(-1) f.w. CONCLUSION No clear effect of fertilisation doses was observed during post-harvest storage on overall quality of fresh-cut baby spinach leaves, while N2O-enriched atmospheres seems to be a promising alternative to passive MAP for extending shelf life.

Inactivation kinetics of foodborne pathogens by UV-C radiation and its subsequent growth in fresh-cut kailan-hybrid broccoli

The inactivation of Escherichia coli, S. Enteritidis and Listeria monocytogenes after UV-C radiation with 0, 2.5, 5, 7.5, 10 and 15 kJ UV-C m(-2) on fresh-cut kailan-hybrid broccoli was explored. Inactivation did not follow linear kinetics. Hence, it was modelled by using the Weibull distribution function, obtaining adjusted R(2) values higher than 94%, indicative of the accuracy of the model to the experimental data. The UV-C doses needed to reduce 1 log cycle the E. coli, S. Enteritidis and L. monocytogenes counts were 1.07, 0.02 and 9.26 kJ m(-2), respectively, being S. Enteritidis the most sensitive microorganism to UV-C radiation while L. monocytogenes was the most resistant. According to experimental data, UV-C doses higher than 2.5 kJ m(-2) did not achieve great microbial reductions. No differences in the growth behaviour of these microorganisms was observed in the treated samples stored under air conditions at 5, 10 and 15 °C, compared to the control. Conclusively, low UV-C doses are effective to reduce E. coli, S. Enteritidis and L. monocytogenes populations in fresh-cut kailan-hybrid broccoli keeping such counts stable during shelf life at 5-10 °C. The current study provides inactivation models for these foodborne pathogens that can be used in microbial risk assessment.

Quality changes of fresh-cut pomegranate arils during shelf life as affected by deficit irrigation and postharvest vapour treatments

BACKGROUND The effect of two sustained deficit irrigation (SDI) strategies, compared to a control, on postharvest physicochemical, microbial, sensory quality attributes and anthocyanin content of fresh-cut pomegranates arils throughout 18 days at 5 °C was studied. Furthermore, the effect of vapour treatments (4, 7 and 10 s) compared to a conventional sanitizing treatment with NaClO on such quality parameters in combination with the preharvest treatments was also studied. RESULTS According to sensory analyses, the shelf life of arils from control and SDI-irrigated fruit was established in 14 and 18 days at 5 °C, respectively, showing 4 and 7 s vapour treatment time the best sensory quality. No significant change was observed in physicochemical quality attributes, across all treatments during storage, while low microbial loads were registered (<3 log CFU g(-1)) after shelf life. Postharvest treatments that had least effect on anthocyanin content on processing day were 7 and 10 s. CONCLUSION Vapour treatments of 7-10 s applied to pomegranate arils led to an extended shelf life up to 18 days at 5 °C with better results in SDI-irrigated samples with a water saving of 6-11%.

Nutritional quality changes throughout shelf-life of fresh-cut kailan-hybrid and ‘Parthenon’ broccoli as affected by temperature and atmosphere composition

The nutritional quality changes of the fresh-cut kailan-hybrid broccoli were compared with those of the ‘Parthenon’ cv. throughout 15 days at 2 ℃, 5 ℃ and 8 ℃ under air and modified atmosphere packaging. Florets showed higher dietary fiber content than stems. The total protein content of kailan-hybrid florets was 2.2-fold higher than that of ‘Parthenon’ cv. and higher amounts of S, Ca, Mg, Fe, Sr, Mn, Zn and Cu were found. However, ‘Parthenon’ florets registered higher initial total phenolics content than the kailan-hybrid edible part, followed by an increase throughout shelf-life favored at 5 ℃ and 8 ℃ under modified atmosphere packaging (5–7 kPa O2 + 14–15 kPa CO2). Modified atmosphere packaging stored samples at 8 ℃ showed higher individual phenolics content than modified atmosphere packaging stored samples at 2 ℃. The initial total antioxidant capacity of the kailan-hybrid edible part was higher than that of ‘Parthenon’ cv. florets. In conclusion, the kailan-hybrid florets generally showed healthier properties on the analyzed bioactive compounds, except total phenolic content, compared to the conventional ‘Parthenon’ cv.

Continuous microwave pasteurization of a vegetable smoothie improves its physical quality and hinders detrimental enzyme activity.

The effect of a pasteurization treatment at 90 ± 2 ℃ for 35 s provided by continuous microwave under different doses (low power/long time and high power/short time) or conventional pasteurization on the quality of orange-colored smoothies and their changes throughout 45 days of storage at 5 ℃ was investigated. A better color retention of the microwave pasteurization- treated smoothie using high power/short time than in conventionally processed sample was evidenced by the stability of the hue angle. The continuous microwave heating increased the viscosity of the smoothie more than the conventional pasteurization in comparison with non-treated samples. Lower residual enzyme activities from peroxidase, pectin methylesterase and polygalacturonase were obtained under microwave heating, specifically due to the use of higher power/shorter time. For this kind of smoothie, polygalacturonase was the more thermo-resistant enzyme and could be used as an indicator of pasteurization efficiency. The use of a continuous semi-industrial microwave using higher power and shorter time, such as 1600 W/206 s and 3600 W/93 s, resulted in better quality smoothies and greater enzyme reduction than conventional thermal treatment.

Preservation of bioactive compounds of a green vegetable smoothie using short time-high temperature mild thermal treatment.

Smoothies represent an excellent and convenient alternative to promote the daily consumption of fruit and vegetables in order to obtain their health-promoting benefits. Accordingly, a green fresh vegetables smoothie (77.2% cucumber, 12% broccoli and 6% spinach) rich in health-promoting compounds was developed. Soluble solids content, pH and titratable acidity of the smoothie were 4.3 ± 0.4°Bx, 4.49 ± 0.01 and 0.22 ± 0.02 mg citric acid 100−1 g fw, respectively. Two thermal treatments to reduce microbial loads and preserve quality were assayed: T1 (3 min at 80 ℃) and T2 (45 s at 90 ℃). Fresh blended unheated samples were used as control (CTRL). The smoothie presented a viscoelastic behaviour. T1 and T2 treatments reduced initial microbial loads by 1.3–2.4 and 1.4–3.1 log units, respectively. Samples were stored in darkness at 5 and 15 ℃. Colour and physicochemical changes were reduced in thermal-treated samples throughout storage, which were better preserved at 5 ℃ rather than at 15 ℃. Vitamin C changes during storage were fitted with a Weibullian distribution. Total vitamin C losses of T1 and T2 samples during storage at 15 ℃ were greatly reduced when they were stored at 5 ℃. Initial total phenolic content (151.1 ± 4.04 mg kg−1 fw) was 44 and 36% increased after T1 and T2 treatments, respectively. The 3-p-coumaroyl quinic and chlorogenic acids accounted the 84.7 and 7.1% relative abundance, respectively. Total antioxidant capacity (234.2 ± 20.3 mg Trolox equivalent kg−1 fw) remained constant after the thermal treatments and was better maintained during storage in thermal-treated samples. Glucobrassicin accounted the 81% of the initial total glucosinolates content (117.8 ± 22.2 mg kg−1 fw) of the smoothie. No glucosinolates losses were observed after T2 treatment being better preserved in thermal-treated samples. Conclusively, a short time–high temperature mild thermal treatment (T2) showed better quality and bioactive compounds retention in a green fresh vegetable smoothie during low temperature storage.

Deficit irrigation strategies combined with controlled atmosphere preserve quality in early peaches

Due to the water scarcity in the Mediterranean countries, irrigation must be optimized while keeping fruit quality. The effect of deficit irrigation strategies on changes in quality parameters of the early “Flordastar” peaches was studied. The deficit irrigation was programmed according to signal intensity of the maximum daily trunk shrinkage; deficit irrigation plants were irrigated to maintain maximum daily trunk shrinkage signal intensity values close to 1.4 or 1.3 in the case of DI1 or DI2 plants, respectively. Results were compared to a control watered at 150% crop evapotranspiration. Fruits were stored up to 14 days at 0 ℃ and 95% Relative Humidity (RH) in air or in controlled atmosphere (controlled atmosphere; 3–4 kPa O2 and 12–14 kPa CO2), followed by a retail sale period of 4 days at 15 ℃ and 90–95% Relative Humidity in air. Weight losses were lower in controlled atmosphere stored peaches from deficit irrigation. Air-stored fruits developed a more intense red color due to a faster ripening, which was not affected by the type of watering. At harvest, deficit irrigation peaches showed higher soluble solids content, which provided a better sensory evaluation. The soluble phenolic content was initially higher (55.26 ± 0.18 mg gallic acid equivalents/100 g fresh weight) and more stable throughout postharvest life in DI1 fruits than in those from the other irrigation treatments. Concerning vitamin C, control fruits at harvest showed higher ascorbic acid than dehydroascorbic acid content (5.43 versus 2.43 mg/100 g fresh weight, respectively), while water stressed peaches showed the opposite results. The combination of DI2 and controlled atmosphere storage allowed saving a significant amount of water and provided peaches with good overall quality, maintaining the bioactive compounds analyzed.

A Fast Molecular Nondestructive Protocol for Evaluating Aerobic Bacterial Load on Fresh-Cut Lettuce

Elaboration of minimally processed or fresh-cut vegetables requires a quick and reliable method for detection of bacterial contamination over the recommended limits. PCR-based methods fulfil these requirements, but amplification from DNA preparations of the food product is often hampered due to inhibiting substances. The purpose of this study was to develop a fast quantitative PCR (qPCR)-based method for aerobic bacterial enumeration in fresh-cut lettuce, using as reference the centrifugation water (CW) that comes up during processing instead of the food matrix itself. Comparisons between bacterial numbers on lettuce leaves before processing and bacterial numbers in the CW both for naturally occurring bacterial populations and for artificially inoculated lettuce were performed. On an average, 35% of the natural bacterial population and 64% of inoculated bacteria were recovered in the CW. Bacterial number in CW was proportional to initial lettuce contamination suggesting that measures on CW allow a narrow estimation of lettuce contamination. In qPCR, a 23S rDNA region was amplified from bacterial DNA present in the CW, followed by melting peak analyses and quantification. Enumeration of cell number by qPCR did not differ significantly from plate assay and might therefore replace it. The proposed protocol, which includes sample taking, DNA extraction and qPCR from the CW can be performed within less than 5 h. The resulting quantification might be used as a proxy of initial lettuce contamination, allowing direct intervention measures before fresh-cut commodity is shipped from the factory.