Strawberry (Fragaria × ananassa Duch.) is one of the most valuable fruits with unique tastes and high nutrient contents. The strawberry rich in anthocyanins can also be used to prevent diabetes, cancer, inflammation, and nervous system diseases. Traditionally, organic solvents are utilized to extract anthocyanins, such as methanol, ethanol and acetone, leading to environmental and health issues, as well as the high costs of solvent removal. Alternatively, the green solvent glycerol has been commonly used in food, cosmetic, and pharmaceutical fields, due to its biodegradability, non-toxicity, and low cost. Furthermore, an acidic environment can also provide for the preservation of anthocyanins, where glycerol was acidified by citric acid. In the present study, a one-step protocol was proposed to extract and preserve the anthocyanins from ‘Benihoppe’ strawberry, according to the four individual factors, such as concentration of glycerol, extraction temperature, liquid-to-solid ratio, and ultrasonic time. Single-factor experiments were first conducted to optimize the extraction, according to the yield of anthocyanins. The response surface method (RSM) was then carried out for further optimization. The anthocyanins were identified from the acidified glycerol extracts using the UPLC-Triple-TOF/MS equipment. A systematic investigation was made to explore the effects of acidified glycerol on the stability of anthocyanins under different temperatures, pH, and light conditions. Moreover, molecular dynamics and quantum chemical calculations were used to clarify the intrinsic mechanism of the extraction and preservation of strawberry anthocyanins by acidified glycerol. The results indicated that the four influencing factors on the yield of anthocyanins were ranked in the descending order of the extraction temperature > ultrasonic time > concentration of glycerol > liquid-to-solid ratio. The yield of anthocyanins was dominated by the individual factors (concentration of glycerol, extraction temperature, and ultrasonic time), interactive factors (concentration of glycerol and extraction temperature), and the quadratic factors (concentration of glycerol, and extraction temperature), according to the ANOVA. RSM results showed the optimal factors were achieved as follows: concentration of glycerol was 26%, extraction temperature was 67 °C, liquid-to-solid ratio was 34 mL/g, and ultrasonic time was 53 min. At the same time, the predicted and actual maximum yield of anthocyanins were (895.38±1.56), and (902.41±0.84) μg/g, respectively. Four anthocyanins were identified by the UPLC-Triple-TOF/MS, including delphinidin-3-glucoside, cyanidin-3-glucoside, pelargonidin-3-glucoside, and malvidin-3-glucoside. The Ultra Performance Liquid Chromatography (UPLC) was also used to quantify the delphinidin-3-glucoside (57.45 μ/g), cyanidin-3-glucoside (125.38 μg/g), pelargonidin-3-glucoside (619.53 μg/g), and malvidin-3-glucoside (96.12 μg/g). Stability tests demonstrated that the acidified glycerol significantly improved the storage stability of anthocyanins under light conditions at high temperatures, compared with the methanol solvent. The molecular dynamics showed the glycerol system shared the larger diffusion coefficient of 0.57 m2/s, a hydrogen bond number of 406, and a smaller intermolecular interaction energy of -1798.85 kcal/mol. In summary, the green solvent of acidified glycerol can be expected to more efficiently extract and preserve anthocyanins from strawberries in industrial applications.
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Edible mushrooms with unique flavor are rich in protein, vitamins, and a variety of bioactive components, such as polysaccharides, phytosterol, etc. China is the major country in the cultivation and consumption of edible mushrooms, among which shiitake mushroom (Lentinula edodes) is the most widely cultivated. The current coolants exhibit low phase change temperature, which may result in chilling injury of shiitake mushrooms.
Based on the freezing temperature of shiitake mushrooms, a novel phase change coolant specially for shiitake mushrooms was developed to maintain the postharvest quality.
The main component of the coolant was screened by differential scanning calorimetry (DSC) based on the phase change latent heat and phase change temperature. Potassium sulfate, nano titanium dioxide, and superabsorbent resin were mixed to prepare the coolant. The effects of coolant on the qualities of shiitake mushrooms were studied by the weight loss rate, color, hardness and other indexes. The activities of enzymes related to glutamate metabolism and energy metabolism were also measured to explore the mechanism of preservation.
The aqueous solution of maltitol was selected as the main component by DSC. The optimal compositions of coolant were 1.85% of maltitol, 2.35% of potassium sulfate, 0.02% of nano titanium dioxide, and 0.80% of super absorbent resin, leading to the phase change latent heat and temperature at 405.26 J·g-1 and -1.8 ℃, respectively. Compared with the control group, under the low-temperature conditions provided by the refrigerant, the weight loss rate of shiitake mushrooms decreased by 51.92%, and the hardness and brightness increased by 66.67% and 41.94%, respectively. The shelf life of shiitake mushrooms was extended. The low temperature also regulated the activities of enzymes, which were related to glutamate metabolism and energy metabolism, the glutamic acid and energy charge level increased by 36.64% and 54.76%, respectively. Finally the freshness of shiitake mushroom was maintained.
The novel phase change coolant based on the freezing temperature of shiitake mushrooms could maintain the weight, color, hardness and other indexes, regulate the level of glutamic acid and energy, and delay the deterioration of shiitake mushrooms. Therefore, the coolant was effective for the cold-chain preservation of shiitake mushrooms.
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