Use of near-infrared spectroscopy and least-squares support vector machine to determine quality change of tomato juice

Near-infrared (NIR) transmittance spectroscopy combined with least-squares support vector machine (LS-SVM) was investigated to study the quality change of tomato juice during the storage. A total of 100 tomato juice samples were used. The spectrum of each tomato juice was collected twice: the first measurement was taken when the tomato juice was fresh and had not undergone any changes, and the second measurement was taken after a month. Principal component analysis (PCA) was used to examine a potential capability of separating juice before and after the storage. The soluble solid content (SSC) and pH of the juice samples were determined. The results show that changes in certain compounds between tomato juice before and after the storage period were obvious. An excellent precision was achieved by LS-SVM model compared with discriminant partial least-squares (DPLS), soft independent modeling of class analogy (SIMCA), and discriminant analysis (DA) models, with 100% of a total accuracy. It can be found that NIR spectroscopy coupled with LS-SVM, DPLS, SIMCA, and DA can be used to control the quality change of tomato juice during the storage.

Antioxidant activity and viability of Lacticaseibacillus rhamnosus, Lacticaseibacillus casei, and Co-culture in fermented tomato juice during refrigerated storage

The fiber content of tomato juice (TJ) may serve as a suitable matrix for protecting probiotics bacteria (PB). The objectives of this study were to: (1) investigate the viability of PB in TJ, namely, Lacticaseibacillus rhamnosus (LG), Lacticaseibacillus casei (LC), and co-culture (LCG) during storage conditions and passing through the gastrointestinal tract and (2) determine the antioxidant activity and physicochemical stability of probiotic tomato juice (TJP) for 20-day refrigerated storage. TJ was separately fermented with single culture LG or LC or co-culture LCG at 37 °C for 72 h. Scanning electron micrographs showed PB immobilized with fibers in TJ, which indicated that PB was protected in TJ. When TJP was exposed to simulated gastric and intestinal fluids, viability was greater than 7 log CFU/mL regardless of the strains after 120 min. Counts for LG, LC, and LCG were 8.7, 8.7, and 9.0 log CFU/mL, respectively, after 20-day storage. TJ without probiotics had the least lycopene content after 20-day storage. The antioxidant capacity of TJP was not significantly different (p < 0.05) after 20-day storage. This study demonstrated that probiotics in the TJP could survive, and TJP maintained the antioxidant activity during the storage.

Enhanced production of thermostable laccases from a native strain of Pycnoporus sanguineus using central composite design

The production of thermostable laccases from a native strain of the white-rot fungus Pycnoporus sanguineus isolated in Mexico was enhanced by testing different media and a combination of inducers including copper sulfate（CuSO4）.The best conditions obtained from screening experiments in shaken flasks using tomato juice,CuSO4,and soybean oil were integrated in an experimental design.Enhanced levels of tomato juice as the medium,CuSO4and soybean oil as inducers（36.8%（v/v）,3 mmol/L,and 1%（v/v）,respectively） were determined for 10 L stirred tank bioreactor runs.This combination resulted in laccase titer of 143000 IU/L（2,2＇-azino-bis（3-ethylbenzthiazoline-6- sulfonic acid）,pH 3.0）,which represents the highest activity so far reported for P.sanguineus in a 10-L fermentor.Other interesting media resulting from the screening included glucose-bactopeptone which increased laccase activity up to 20000 IU/L,whereas the inducers Acid Blue 62 and Reactive Blue 19 enhanced enzyme production in this medium 10 times.Based on a partial characterization,the laccases of this strain are especially promising in terms of thermostability（half-life of 6.1 h at 60 °C） and activity titers.