Taking the Yali and Xuehua pears as the objects, this study aims to clarify the physicochemical indexes and volatile components under impact damage stress. A simple sliding with the inclined plane was self-constructed to induce the impact on the pears. The samples were prepared with the invisible and visible damages after the different durations. Gas chromatography-ion mobility spectrometry was used to identify the volatile components of the pears at different damage times for various varieties. The characteristic volatiles were identified after the impact damage. The results showed that the enzymatic browning gradually occurred in the damaged area, thus causing the dark color to eventually turn into a yellowish-brown hue. Furthermore, the L* value of the peel decreased, as the damage time extended, while the b* value increased; The hardness also exhibited a downward trend. The cell wall was formed after the gradual dissolution of the pectin within cells and cellulose, as well as the destruction of cell structure integrity. The cell collapse was then caused by the outflow of cell sap. The content of the soluble solids shared a decreasing trend. While there was an increase in the content of the titratable acidity; The hydrolysis of the sugar substances within fruit cells converted them into alcohols, acids, and non-sugar substances. The alcohol substances were also gradually turned into acids under the microorganisms and enzymes. The fingerprint maps of the pears with the different damage degrees were established to visualize the volatile components among various categories of samples. Principal component analysis further demonstrated that the healthy samples were effectively distinguished from those with varying degrees of damage, according to the volatile components after detection. The volatile components were identified between the varieties of pears. There were 45 volatile components in the Yali pear samples, including 10 alcohols, 10 esters, 4 aldehydes, 4 acids, 4 ketones, 3 amines, 3 alkanes, 2 pyrazines, 2 furans, 1 pyrrole, 1 thiazole, and 1 nitrile. Healthy Yali pears primarily contained the esters and alcohols, with the higher contents of (E)-2-hexen-1-ol and acetic acid ethyl ester; The healthy Xuehua pears were composed mainly of alcohols, with the higher contents of oct-1-en-3-ol, 3-octanol, and (E)-2-hexen-1-ol. Furthermore, the contents of the alcohols and aldehydes increased after impact damage. Among them, 23 aroma compounds shared the VIP>1, including 1 aldehyde, 1 amine, 3 ketones, 7 alcohols, 3 acids, 4 esters, and 4 heterocyclic compounds. A Venn diagram was combined to identify the characteristic volatiles for the Yali and Xuehua pears in different states: The healthy state was featured by methyl 3-methylbutanoate and N, N-diethylethylamine; While the invisible damage state was characterized by the heptanal and dihydro-2(3H)-furanone; And the visible damage was featured by propionic acid and 2-pentylfuran. In Xuehua pears, 86 volatile components were identified, including 20 alcohols, 17 esters, 7 aldehydes, 7 ketones, 6 amines, 6 alkanes, 6 pyrazines, 5 acids, 5 ethers, 3 nitriles, 1 pyridine, 1 furan, 1 thiazole, and 1 thiophene. Fifty-one aroma compounds shared the VIP>1, including 6 aldehydes, 5 ketones, 14 alcohols, 4 acids, 13 esters, 2 amines, and 7 heterocyclic compounds. In Xuehua pears, the healthy state was featured by (Z)-3-nonen-1-ol and 2-ethyl-5-methylpyrazine; while the invisible damage state was characterized by the pentanoic acid N-amyl butyrate and (E)-2-pentenal; and the visible damage was featured by acetic acid ethyl ester and 3-methyl-2-isobutyl pyrazine. There were the great effects of the mechanical damage stress on two types of pears' main physicochemical indicators. The characteristic volatiles of impact damage were clarified after evaluation. The finding can provide a theoretical basis for diagnosing and recognizing mechanical damage in pears using olfactory sensors.

In order to investigate the intrinsic relationship between protein characteristics and quality changes during the hot air drying of shrimp, Penaeus vannamei was dried by hot air at 55 ℃ after being boiled in 3% salt solution for 2 minutes. We studied changes in the microstructure and quality of shrimp, and systematically investigated changes in the oxidative degradation degree, intramolecular valence bonds, and secondary and tertiary structure of protein. The results showed that the drying treatment gradually decreased the L*, a* and b* values of shrimp, and changed the texture characteristics, and the hardness, adhesiveness and chewiness were increased to 344.78 N, 45.01 mJ and 116.50 mJ at the end of drying, respectively. In addition, oxidative denaturation and degradation of proteins occurred; the total sulfhydryl content decreased to 0.36 μmol/g at the end of drying, while the carbonyl content increased to 2.03 nmol/mg protein, and the trichloroacetic acid (TCA)-soluble peptide content increased to 0.91 μmol/g. The protein structure was significantly changed; the relative contents of ionic and hydrogen bonds decreased, the relative contents of hydrophobic and disulfide bonds increased, the secondary structure was transformed from α-helix to β-fold, β-turn and random coil, the intensity of tryptophan fluorescence decreased, and the tertiary structure was also changed. Pearson correlation analysis showed that the color changes were mainly related to protein oxidation and protein degradation and denaturation significantly affected the textural properties of shrimp. This study can provide theoretical support for further improving the quality of dried shrimp products.