Volatile organic compounds (VOCs) make up milk flavor and are essential attributes for consumers to evaluate milk quality. In order to investigate the influence of heat treatment on the VOCs of milk, electronic nose (E-nose), electronic tongue (E-tongue) and headspace solid-phase microextraction (HS-SPME)–gas chromatography–mass spectrometry (GC-MS) technology were used to evaluate the changes in VOCs in milk during 65 °C heat treatment and 135 °C heat treatment. The E-nose revealed differences in the overall flavor of milk, and the overall flavor performance of milk after heat treatment at 65 °C for 30 min is similar to that of raw milk, which can maximize the preservation of the original taste of milk. However, both were significantly different to the 135 °C-treated milk. The E-tongue results showed that the different processing techniques significantly affected taste presentation. In terms of taste performance, the sweetness of raw milk was more prominent, the saltiness of milk treated at 65 °C was more prominent, and the bitterness of milk treated at 135 °C was more prominent. The results of HS-SPME-GC-MS showed that a total of 43 VOCs were identified in the three types of milk—5 aldehydes, 8 alcohols, 4 ketones, 3 esters, 13 acids, 8 hydrocarbons, 1 nitrogenous compound, and 1 phenol. The amount of acid compounds was dramatically reduced as the heat treatment temperature rose, while ketones, esters, and hydrocarbons were encouraged to accumulate instead. Furfural, 2-heptanone, 2-undecanone, 2-furanmethanol, pentanoic acid ethyl ester, 5-octanolide, and 4,7-dimethyl-undecane can be used as the characteristic VOCs of milk treated at 135 °C. Our study provides new evidence for differences in VOCs produced during milk processing and insights into quality control during milk production.

The flavor of fresh, raw milk is considered to be the key to maintaining the quality of dairy products, and is very crucial in affecting a consumer’s choice. To better understand the differences in flavor of fresh milk between feeding patterns, we conducted the following study. Twelve Holstein cows reared in pure grazing mode and twelve reared intensively in medium to large farms were selected from the Xinjiang Uygur Autonomous Regions at the same time, and the flavor of their raw milk was analyzed. Aroma profiles and taste attributes were assessed by electronic nose and electronic tongue, respectively, and volatile flavor compounds were characterized and quantified by Headspace-Solid Phase Microextraction/Gas Chromatography-Mass Spectrometry. Thirteen volatile compounds were identified in the indoor feeding pattern and 12 in the grazing; most of them overlapped. W1S, W2S and W5S were the main contributing sensors of the electronic nose for the overall assessment of the aroma profile. Raw milk from grazing had more intense astringency, bitterness, sourness and richness in taste compared to indoor feeding. Different dietary conditions may contribute to a variety of aroma profiles. Oxime-, methoxy-phenyl-, octadecanoic acid, furfural and dodecanoic acid were the key volatile flavor compounds of grazing. Meanwhile, raw milk from indoor feeding patterns was unique in 2-nonanone, heptanoic acid and n-decanoic acid. All three detection techniques were valid and feasible for differentiating raw milk in both feeding patterns, and the compounds were significantly correlated with the key sensors by correlation analysis. This study is promising for the future use of metabolic sources of volatile organic compounds to track and monitor animal feeding systems.

In northern China, plastic-shed vegetable production significantly contributes to nitrogen (N)-induced groundwater eutrophication due to excessive fertilization and irrigation. However, the impact of optimized farming practices on N leaching has seldom been systematically examined. We conducted a four-season field study to evaluate the impacts of optimal farming measures on tomato yield, water percolation, N concentration in leachate, and total N (TN) leaching. The treatments included conventional fertilization and flood irrigation (CON), fertilization decreased by 20% and flood irrigation (OPT1) or drip fertigation (OPT2), fertilization decreased by 30% and drip fertigation (OPT3), and no fertilization with flood irrigation (CK). Compared with the CON treatment, the optimal treatments significantly reduced annual TN leaching by 9.92–50.7% without affecting tomato yield (57.1–98.2 t ha⁻¹ for CON and 48.1–106 t ha⁻¹ for three optimal treatments). Drip irrigation contributed 73.8–79.0% to the mitigation of TN leaching. The N originating from soil and irrigation water exhibited a similar contribution to TN leaching (45.4–58.6%) to that of fertilizer N. The daily TN leaching at the basal fertilization stage was much greater than that at the top-dressing stage, due to over-fertilization. Optimizing fertilization, particularly basal fertilization, in combination with drip irrigation could substantially reduce N leaching in plastic-shed vegetable production. Other optimal practices, such as decision support systems (DSSs) and fertilizer amendments, could also be investigated to further mitigate the N leaching.