Enhancing the hardness of potato slices after boiling by combined treatment with lactic acid and calcium chloride: Mechanism and optimization

The influence of pH and calcium ions on the gelation of low methoxy pectin from potato

In this study, pectin was extracted from potato with the hydrolysis of cellulose, as well as its acid-induced and Ca2+-induced gelation behavior was investigated, too. The gelation process of unhydrolyzed pectin might be used as a model for studying the gelation behavior and characteristic of pectin within the cell wall. The results showed that potato pectin solution (3%) could form a gel state at a minimal concentration of 0.25% CaCl2 or a maximum pH value of 4.60. Furthermore, acetic acid-induced and CaCl2-induced gels were both concentration-independent. Specifically, the gel strength increased with decreasing levels of pH and increasing concentrations of CaCl2. Moreover, CaCl2-induced gels exhibited superior gelation characteristics with a higher storage modulus (7.2 Pa), larger fractal dimension (2.58), smaller porosity (12.11%), shorter relaxation time T2, and a denser gel network structure. This disparity stemmed from different mechanism: acetic acid provided H+ to combine with free carboxyl groups on the pectin chains, reducing the repulsion between pectin molecules, narrowing chain spacing, and fostering hydrogen bond formation; whereas CaCl2 promoted gelation primarily via the information of the "egg box" structure involving non-covalent bonded calcium bridges. This research could provide a theoretical basis for acid-induced and Ca2+-induced gelation of unhydrolyzed pectin extracted from the cell wall.

Lemon juice pretreatment as a strategy to preserve the quality and enhance the texture of cooked potato slices of different sizes

Potatoes are an important food crop worldwide and are rich in essential nutrients. However, cooking can reduce their nutritional value and alter their texture. This study aimed to investigate the impact of pretreating potato slices with lemon juice. The slices were immersed in 5% lemon juice solution for 3 h, rinsed with distilled water for another 3 h, then cooked at 100°C for 20 min. Findings revealed that lemon juice pretreatment (LJP) notably improved the texture, mouthfeel, and overall acceptability of the cooked potato slices of different sizes (CPS-Ds). Additionally, LJP significantly increased vitamin C and total phenolic contents, slightly decreased pH levels, and preserved the desired color of CPS-Ds. Consumer sensory evaluations also indicated a positive response to LJP samples, suggesting its potential application in the food industry. The study confirmed that LJP is an effective, sustainable, consumer-friendly, and cost-efficient technique for improving the quality of cooked potato slices.

The texture of potato mashes is impacted by blanching induced changes in their extracellular starch fractions

The texture of potato mash significantly influences consumer satisfaction. We here investigated the impact of blanching and different methods thereof on the texture and extractable extracellular fractions (EEFs) of potato mash when extracted with water or with dimethyl sulfoxide (DMSO) to seek determining factors of potato mash texture. Mashes prepared from potatoes blanched in 2.04 mM CaCl2 (CaB-M) exhibited hardness (24.9 N) and stickiness (1.0 N·s) readings intermediate to those from potatoes that were not blanched (NB-M, 19.2 N and 1.2 N·s), or blanched in deionized water (WaB-M, 30.5 N and 0.6 N·s), which aligned with their levels of intact cells. Starch was the main constituent (57.2 % - 64.4 %, w/w) in all EEFs and more starch was present in (1) NB-M and (2) the DMSO extracts. The chain length distributions of DMSO-extracted extracellular starch (DEES) revealed that the amylopectin content increased in the order WaB-M (46.3 %), CaB-M (55.1 %), and NB-M (76.6 %), which was attributed to more intracellular amylopectin being released to the extracellular phase of mashes. The relative contents of shorter chain amylose (degree of polymerization 110-1000) and the DEES yield were significantly correlated to the hardness while the yield of DEEFs was positively correlated with the stickiness.

Assessment of the Content of Glycoalkaloids in Potato Snacks Made from Colored Potatoes, Resulting from the Action of Organic Acids and Thermal Processing

Glycoalkaloids (TGAs, total glycoalkaloids), toxic secondary metabolites, are found in potatoes (110-335 mg·kg-1 DW), mainly in the peel. Colorful, unpeeled potatoes are an innovative raw material for the production of snacks which are poorly tested in terms of their glycoalkaloid content. Third-generation snacks and French fries made from red-fleshed Mulberry Beauty (MB) and purple-fleshed Double Fun (DF) potatoes were produced with the use of 1% solutions of ascorbic, citric, lactic, malic, and tartaric acids to stabilize the structure of anthocyanins in the raw material and maintain their color in obtained products. The influence of the type of acid and thermal processes, like frying, microwaving, and baking, on the content of glycoalkaloids in ready-made products was examined. Only 0.45-1.26 mg·100 g-1 of TGA was found in pellet snacks and 1.32-1.71 mg·100 g-1 in French fries. Soaking blanched potatoes in organic acid solution reduced the α-chaconine content by 91-97% in snacks and by 57-93% in French fries in relation to the raw material to the greatest extent after the use of malic acid and the DF variety. The effect of lactic and citric acid was also beneficial, especially in the production of baked French fries from MB potatoes.

Assessment of cell wall degrading enzymes by molecular docking and dynamics simulations: Effects of novel infrared treatment

Cell wall-degrading enzymes' activities under infrared treatment are vital for peeling; it is critical to elucidate the mechanisms of the novel infrared peeling in relation to its impact on cell wall-degrading enzymes. In this study, the activities, and gene expressions of eight degrading enzymes closely related to pectin, cellulose and hemicellulose were determined. The most influential enzyme was selected from them, and then the mechanism of its changes was revealed by molecular dynamics simulation and molecular docking. The results demonstrated that infrared had the most significant effect on β-glucosidase among the tested enzymes (increased activity and up-regulated gene expression of 195.65 % and 7.08, respectively). It is suggested infrared crucially promotes cell wall degradation by affecting β-glucosidase. After infrared treatment, β-glucosidase's structure moderately transformed to a more open one and became flexible, increasing the affinity between β-glucosidase and substrate (increasing 75 % H-bonds and shortening 15.89 % average length), thereby improving β-glucosidase's activity. It contributed to cell wall degradation. The conclusion is that the effect of infrared on the activity, gene expression and molecular structure of β-glucosidase causes damage to the peel, thus broadening the applicability of the new infrared dry-peeling technique, which has the potential to replace traditional wet-peeling methods.

Insights into the Acid-Induced Gelation of Original Pectin from Potato Cell Walls by Gluconic Acid-δ-Lactone

The acid-induced gelation of pectin in potato cell walls has been gradually recognized to be related to the improvement in the cell wall integrity after heat processing. The aim of this study was to characterize the acid-induced gelation of original pectin from a potato cell wall (OPP). Rheological analyses showed a typical solution-sol-gel transition process of OPP with different additions of gluconic acid-δ-lactone (GDL). The gelation time (Gt) of OPP was significantly shortened from 7424 s to 2286 s. The complex viscosity (η*) of OPP gradually increased after 4000 s when the pH was lower than 3.13 and increased from 0.15 to a range of 0.20~6.3 Pa·s at 9000 s. The increase in shear rate caused a decrease in η, indicating that OPP belongs to a typical non-Newtonian fluid. Furthermore, a decrease in ζ-potential (from -21.5 mV to -11.3 mV) and an increase in particle size distribution (from a nano to micro scale) was observed in OPP after gelation, as well as a more complex (fractal dimension increased from 1.78 to 1.86) and compact (cores observed by cryo-SEM became smaller and denser) structure. The crystallinity of OPP also increased from 8.61% to 26.44%~38.11% with the addition of GDL. The above results call for an investigation of the role of acid-induced OPP gelation on potato cell walls after heat processing.

Acetic Acid Immersion Alleviates the Softening of Cooked Sagittaria sagittifolia L. Slices by Affecting Cell Wall Polysaccharides

This study investigated the mechanism for acetic acid pretreatment to improve cell wall integrity and thereby enhance the hardness of cooked Sagittaria sagittifolia L. slices by affecting polysaccharides in the cell wall. Distilled water immersion and 0.6% acetic acid immersion (the solid/liquid ratio is 1:10) for 15 h at room temperature could result in the conversion of pectin through different reactions during thermal processing. Combined in situ and in vitro analysis demonstrated that acetic acid pretreatment could promote the interaction of cellulose microfiber or hemicellulose with RG-Ⅰ side chains during thermal processing of S. sagittifolia L. slices, promote the entanglement between linear pectin molecules and make hemicellulose show a lower molecular weight under cooking, making it easy to firmly bind to pectin, which resulted in texture changes. The findings may help improve the texture of thermally processed vegetables and fruits and deep processing of starchy vegetables.

Citral Essential Oil-Loaded Microcapsules by Simple Coacervation and Its Application on Peach Preservation

Citral essential oil (CEO) was encapsulated by the single coalescence method, and its stability, release properties, and ability to maintain freshness were evaluated for the first time. The microshape characteristics of a CEO-loaded microcapsule (CM) were analyzed by inverted microscopy (OM) and scanning electron microscopy (SEM). The encapsulation efficiency, stability, and release behavior of CEO were evaluated using Fourier transform infrared spectroscopy (FTIR), thermogravimetric/differential thermal comprehensive analysis (TG/DSC), and gas chromatography mass spectrometry (GC/MS). Moreover, peaches were used to evaluate the preservation properties of the CEO-loaded microcapsule. The results showed that the microcapsule produced using simple coacervation had better microstructure and the ability to reduce and control the release of citral essential oil. The qualities of peaches, such as appearance changes, hardness, soluble solid content, total acids, and total bacterial counts, were significantly improved in the CM system during storage, in comparison with the control and cold storage groups. Therefore, the CM has potential applications and development prospects in the food, drug, and other industries.

Potato Processing Industry in China: Current Scenario, Future Trends and Global Impact

Potatoes play an important role in ensuring food security. During the COVID-19 epidemic, consumption of processed potato products decreased, and consumption of fresh potatoes increased. China is the world's largest potato producer with more than 4.81 million hectares of area under potato production and 90.32 million metric tonnes of potatoes produced in 2018. This accounts for 27.36% of the world's planting area and 24.53% of the world's potato production. The proportion of potatoes processed in China was about 12% in 2017, mostly dominated by starch production. However, the recent policy of the Chinese government to popularise potato as a staple food has created new markets for processed potato products other than starch. A very few reports have analysed these future trends of the rapidly growing Chinese potato processing industry and its impact within and outside China. This paper provides an overview of the latest developments with a focus on processed potato products such as potato chips, French fries and dehydrated potatoes, and also, due to the unique Chinese diet culture, it highlights the need for more scientific research dedicated towards the development of novel potato-based healthy foods.

Evaluation of cooking, nutritional, and quality characteristics of fresh-cut potato slice pretreated with acetic acid

Fresh-cut potato slices are very popular in the service of hot-pots. However, the gelatinized starch easily escaping from the potato cells during cooking causes the thickening of beef tallow or soup in the hot-pot. Thus, acetic acid is considered for solving the problem of potato slices. Besides, the nutritional and quality characteristics of potato slices are also evaluated in this study. Results show that 1.0%-1.5% (v/v) acetic acid treatment can decrease mass loss and starch digestion rate, and delay the degradation of ascorbic acid and deterioration of color and texture of potato slices. Such treatment also inhibits membrane oxidation and PPO activity, and increase the total phenolic accumulation of potato slice in 7-day storage. The cell wall integrity of the potato slice is strengthened by acetic acid treatment, providing a strategy for the improvement of the boiling resistance of potato slice, and endowing potato slice with the digesting resistance. PRACTICAL APPLICATION: Acid pretreatment would cause the intensification of potato cell wall, which finally decrease the in vitro digestibility through decrease of leakage of gelatinized starch from potato cell and the contact between gelatinized starch and digesting enzyme. This observation proved that the integrity of cell structure in vegetable is important for their processing quality improvement (especially for their hardness improvement after heating or fermentation).

Effects of Breaking Methods on the Viscosity, Rheological Properties and Nutritional Value of Tomato Paste

Ultrasound-assisted processing has potential application advantages as an emerging technology for preparing tomato paste. This work explored the influence of ultrasound break at 22 °C (US-Break-22) and 65 °C (US-Break-65) on the viscosity, rheological properties and nutritional values of newly prepared tomato paste, compared with traditional thermal break at 65 °C (Break-65) and 90 °C (Break-90). Results showed that the US-Break-65 paste had the largest apparent viscosity, yield stress, consistency coefficient, solid-like nature, and large amplitude oscillatory shear behavior, followed by the US-Break-22 paste, Break-90 paste, and Break-65 paste. Based on the results of the pectin-related enzymes, particle size, and serum pectin of the pastes, it was revealed that the above-mentioned properties were mainly determined by the particle size and pectin content in their serum. The level of ascorbic acid followed the order of US-Break-22 paste > US-Break-65 paste > Break-65 paste > Break-90 paste. The level of total carotenoids followed the order of US-Break-22 paste ≈ US-Break-65 paste > Break-90 paste ≈ Break-65 paste. The level of total cis-carotenoids followed the order of US-Break-65 paste > US-Break-22 paste > Break-90 paste > Break-65 paste. The level of phenolics and antioxidant activities followed the same order of US-Break-22 paste > US-Break-65 paste > Break-90 paste > Break-65 paste. Overall, the viscosity, rheological properties and nutritional values of the tomato pastes prepared by US-Break-65 and US-Break-22 were significantly higher than those prepared by Break-65 and Break-90. Therefore, ultrasound assisted processing can prepare high quality tomato paste and can be widely implemented in the tomato paste processing industry.

Effects of tissue pre-degassing followed by ultrasound-assisted freezing on freezing efficiency and quality attributes of radishes

The rapid freezing technique for porous foods using tissue pre-degassing followed by ultrasound-assisted freezing (UF) was developed, and its effects on quality attributes of radishes including tissue air volume, hardness, total calcium contents, bonded calcium contents, retention rates of bonded calcium and microstructures were investigated. To evaluate the freezing efficiency, parameters including total freezing time, phase transition time, and the increases of freezing rate and phase transition rate were determined. Besides, multivariate statistical analyses including principal component analysis (PCA) and hierarchical cluster analysis (HCA) were performed to visualize and further analyze the quality differences of radishes under different treatments. Results suggested that decreasing tissue air volumes can significantly shorten the phase transition time of UF. Samples treated by pre-degassing for 5 min at -0.09 MPa followed by UF (D_-0.09MPa^5min-UF) showed the freezing rate and phase transition rate increased by 28.8% and 29.8%, respectively, as compared with the same pre-degassed samples frozen by immersion freezing (D_-0.09MPa^5min-IF). Retention rates of bonded calcium positively correlated with the sample hardness, announcing the importance of bonded calcium maintenance during radish freezing. Both PCA and HCA indicated that D_-0.09MPa^5min-UF endowed radishes with quality attributes more similar to the fresh ones, which was further verified by microstructure analysis, showing remarkably alleviated plasma membrane puncture, cell separation and deformation in D_-0.09MPa^5min-UF samples. The current study proved that the technique of tissue pre-degassing followed by UF could effectively improve the freezing efficiency and quality attributes of frozen radishes, and thus have great potentials in rapid freezing of porous foods.

Effect of polysaccharides on the gel characteristics of "Yu Dong" formed with fish (Cyprinus carpio L.) scale aqueous extract

A novel protein-based gel named "Yu dong" prepared with fish (Cyprinus carpio L.) scale aqueous extract and enhanced by polysaccharides is described in this study. The effects of pectin, alginate, and sodium carboxyl methyl cellulose (CMC-Na) on FS gel formation, stability, textural characteristics, microstructure, and water distribution were evaluated. The results indicated the viscosity of the FS gels decreased and changed slowly as the addition of pectin. While, the addition of alginate enhanced the formation of FS gels. As pectin addition in FS gels, the transition temperature decreased. When alginate and CMC-Na was added to the FS gels, the transition temperature increased. The addition of pectin, alginate, and CMC-Na to the FS gels significantly increased G_r from 44.5% to 71.99%, 61.86%, and 71.35%, respectively. Gel strength increased significantly as the addition of pectin, alginate, and CMC-Na. LF-NMR results showed that a moderate amount (0.2%) of polysaccharides bonded the protein and water more tightly, which was consistent with the SEM results showing gel structure with more uniform pores. This study provides a direct application of FS protein in preparing of gel food, which showing a better way to utilize the abandoned fish resource.