Evaluation of quality changes of differently formulated cloudy mixed juices during refrigerated storage after high pressure processing

Inactivation mechanisms on pectin methylesterase by high pressure processing combined with its recombinant inhibitor

High pressure processing (HPP) juice often experiences cloud loss during storage, caused by the activity of pectin methylesterase (PME). The combination of HPP with natural pectin methylesterase inhibitor (PMEI) could improve juice stability. However, extracting natural PMEI is challenging. Gene recombination technology offers a solution by efficiently expressing recombinant PMEI from Escherichia coli and Pichia pastoris. Experimental and molecular dynamics simulation were conducted to investigate changes in activity, structure, and interaction of PME and recombinant PMEI during HPP. The results showed PME retained high residual activity, while PMEI demonstrated superior pressure resistance. Under HPP, PMEI's structure remained stable, while the N-terminus of PME's α-helix became unstable. Additionally, the helix at the junction with the PME/PMEI complex changed, thereby affecting its binding. Furthermore, PMEI competed with pectin for active sites on PME, elucidating. The potential mechanism of PME inactivation through the synergistic effects of HPP and PMEI.

Effects of Pulsed Electric Field and High-Pressure Processing Treatments on the Juice Yield and Quality of Sea Buckthorn

Sea buckthorn juice has high nutritional value and a rich flavor that consumers enjoy. Traditional sea buckthorn thermal processing (TP) technology has problems such as low juice yield, poor quality, and poor flavor. Sea buckthorn berries are processed using a technique combining pulsed electric field (PEF) and high-pressure processing (HPP) to increase juice yield and study its impact on the quality and volatile aroma of sea buckthorn juice. Results have show that, compared with TP, under the condition of PEF-HPP, the juice yield of sea buckthorn significantly increased by 11.37% (p > 0.05); TP and PEF-HPP treatments could effectively kill microorganisms in sea buckthorn juice, but the quality of sea buckthorn juice decreased significantly after TP treatment (p > 0.05), whereas PEF-HPP coupling technology could maximally retain the nutrients of sea buckthorn juice while inhibiting enzymatic browning to improve color, viscosity, and particle size. The flavor of sea buckthorn juice is analyzed using electronic nose (E-nose) and gas chromatography-ion mobility spectrometer (GC-IMS) techniques, and it has been shown that PEF-HPP retains more characteristic volatile organic compounds (VOCs) of sea buckthorn while avoiding the acrid and pungent flavors produced by TP, such as benzaldehyde, (E)-2-heptenal, and pentanoic acid, among others, which improves the sensory quality of sea buckthorn juice. PEF-HPP technology is environmentally friendly and efficient, with significant economic benefits. Research data provide information and a theoretical basis for the sea buckthorn juice processing industry.

Effect of a Biosurfactant Extract Obtained from a Corn Kernel Fermented Stream on the Sensory Colour Properties of Apple and Orange Juices

In this work, we assessed the effect of a biosurfactant extract, which possesses preservative properties, on the sensory properties, regarding colour, of two fruit juices: pasteurized apple juice and natural orange juice. This biosurfactant extract was obtained from corn steep liquor, a secondary stream of the corn wet-milling industry. The biosurfactant extract is composed of natural polymers and biocompounds released during the spontaneous fermentation of corn kernels during the steeping process of corn. The reason for this study is based on the importance of colour as a visual attribute that can determine the consumer's preferences; it is important to study the effect of the biosurfactant extract under evaluation before including it in juice matrices. For this, a surface response factorial design was employed and the effects of the biosurfactant extract concentration (0-1 g/L), the storage time (1-7 days), and the conservation temperature (4-36 °C) on the CIELAB colour parameters (L*, a*, b*) of the juice matrices were evaluated, as well as the total colour differences (ΔE*) regarding the control juices and the saturation index (Cab*). Moreover, the CIELAB coordinates of each conducted treatment were converted into RGB values to obtain visual colour differences that can be appreciated by testers or consumers.

A Novel Strategy to Improve Cloud Stability of Orange-Based Juice: Combination of Natural Pectin Methylesterase Inhibitor and High-Pressure Processing

This study investigated the prospect of producing cloud-stable orange-based juice by combining high-pressure processing (HPP) with a natural kiwifruit pectin methylesterase inhibitor (PMEI) during chilled storage. Kiwifruit is rich in a PMEI, which greatly improves the cloud loss caused by the pectin methylesterase (PME) demethylation of pectin. The results show that the cloud loss of orange juice occurred after 3 days, while the orange-kiwifruit mixed juice and kiwifruit puree were cloud stable during 28 days' storage. Although, the kiwifruit puree contained larger particles compared to the orange juice, its higher viscosity and solid-like behavior were dominant, improving the cloud stability of the juice systems. In addition, the particle size distribution and rheological properties were highly related to PME activity, PMEI activity, and pectin characterization. The kiwifruit PMEI showed higher resistance to HPP and storage time than PME. More water-solubilized pectin fractions with a high molecular mass were found in the kiwifruit puree, leading to its high viscosity and large particle size, but a more chelator-solubilized pectin fraction with a low esterification degree was observed in the orange juice, resulting in its cloud loss. In general, the outcome of this work provides a novel strategy to improve the cloud stability of orange-based juices using natural PMEIs and nonthermal processing technologies.

Effect of a Multifunctional Biosurfactant Extract Obtained from Corn Steep Liquor on Orange and Apple Juices

Biosurfactant extracts are multifunctional ingredients composed of natural polymers that can be used in the food industry as stabilizing and antimicrobial agents, although their inclusion in food matrices has been scarcely explored. In this work, a biosurfactant extract, with antimicrobial properties, obtained from a fermented stream of the corn wet-milling industry was introduced into an apple and orange juice matrix to evaluate the changes produced in the sugar consumption, pH, and biomass formation at different temperatures (4–36 °C) and storage time (1–7 days). It was observed that the addition of biosurfactant extract reduced the hydrolysis rate of polymeric sugars, decreasing the concentration of soluble sugars from 85.4 g/L to 49.0 g/L in apple juice after 7 days at 20 °C in the absence and presence of biosurfactant extract, respectively. In general, soluble sugars increased in juices for 5–6 days and after those sugars decreased at different rates depending on the temperature of storage. Differences in sugar solubilization and degradation were more significant in apple juice than in orange juice at 20 °C and 7 days of storage, achieving for orange juice values of 101 and 102 g/L in the absence and presence of biosurfactant extract, respectively. Biomass growth was almost unaffected by the biosurfactant extract concentration and the optimal conditions for biomass production were detected at intermediated temperatures after 6–7 days of storage for both apple and orange juices, obtaining maximum concentrations of 1.68 g/L and 1.54 g/L for apple juice and orange juice, respectively, in the absence of biosurfactant extract. The pH during storage was kept in the range of 3.35–3.48 for apple juice and of 3.40–3.77 for orange juice.

Role of pectin characteristics in orange juice stabilization: Effect of high-pressure processing in combination with centrifugation pretreatments

"High-pressure processing (HPP) plus" combined technologies are applied to overcome the limitation of single HPP and to produce juices with more stable quality during storage. This research explored the potential of HPP in combination with centrifugation to produce cloud stable orange juice during refrigerated storage. The results indicated that HPP combined processing technology significantly improved the cloud stability of orange juice, which was related to removed large particles, reduced viscosity, decreased protein contents, and inactivated pectin methylesterase activity induced by centrifugation (P < 0.05). Besides, chelator solubilized pectin (CSP) decreased but water solubilized pectin (WSP) maintained in the juice after centrifugation. During storage, the conversion of pectin fraction from WSP to CSP, resulting in sedimentation appeared in centrifugation treated orange juice when stored for 28 days. In general, pectin characteristics changes and pectin fractions conversion were the main driving forces affecting cloud stability of orange juice pasteurized by HPP in combination with centrifugation and during chilled storage.