Freshly prepared Lueyang black-bone chicken meatballs were purchased from Shaanxi Longjia Agricultural Technology Co., Ltd. (Hanzhong, China). To maintain sample freshness and uniformity, all the meatballs were analyzed on the day of purchase without undergoing freezing. Before being subjected to sensory evaluation and GC–IMS analysis, the samples were stored at 4 ± 1°C for a maximum of 6 h. The ingredients were sourced from a local supermarket and included black-bone chicken meat, spices, food additives (monosodium glutamate, sodium tripolyphosphate, sodium hexametaphosphate, sodium hexametaphosphate, carrageenan), and chicken powder seasoning, along with starch, soybean protein, edible salt, and white sugar. Standard n-ketones were purchased from Guoyao Chemical Co., Ltd. (Shanghai, China).

Chicken meatballs were prepared according to previous method Aydemir et al. (24, 25), with slight modifications. Uniform black-bone chicken meatball samples were selected for preliminary testing. On the basis of the preliminary experiment and sensory evaluation, the optimal texture of the meatballs was achieved after 6 min of cooking. Prolonged cooking beyond this duration adversely affects the color and texture of meatballs while also causing a loss or destruction of nutritional components. Under these conditions, the meatballs demonstrated optimal overall quality, reflected by the highest sensory evaluation scores and favorable instrumentally measured color and texture parameters. Therefore, the single-factor experimental time was set to 6 min. After thawing and weighing, black-bone chicken meatballs were prepared via three different cooking techniques. For the boiling method, the meatballs were subjected to boiling water at 2100 W for 6 min, cooled, air-dried until moisture-free, and reweighed. For steaming, the samples were steamed at the same power for 6 min (C22-RT22E01, Midea Group Co. Ltd., China), followed by cooling and air drying before being weighed again. For frying, the meatballs were coated with rapeseed oil, air dried at 180°C for 6 min, and then reweighed. For each cooking method, three meatballs were prepared and analyzed, each with an approximate radius of 1.5 ± 0.2 cm. During frying, the meatballs were cooked over medium heat for 6 min in total—approximately 3 min per side—while being turned regularly to ensure uniform cooking.

Sensory evaluation of meatballs prepared through different cooking methods followed the standards outlined in SB/T 10610–2011. The sensory evaluation criteria for black-bone chicken meatballs (Supplementary Table S1) included assessments of color, taste, texture, and juiciness. Twenty trained sensory panelists (10 males and 10 females, aged 20–22 years), all undergraduate students, were recruited to evaluate the meatballs on the basis of the specified quality attributes.

An SR-62 colorimeter (3nh Technology Co., Shenzhen, China) was used according to the method of Gui et al. (26). Three parallel groups were measured for each sample, and six points per group were analyzed. The results were averaged. For the meatballs prepared via different cooking methods, the surface water and oil of the black-bone chicken meatballs were absorbed via absorbent paper. A portable colorimeter was used to quantify the L* (lightness), a* (redness), and b* (yellowness) values.

In accordance with the methods of Li et al. (27), texture was determined via a Brookfield CT3 texture analyzer (Brookfield, United States). The parameters used were as follows: TA39 probe, with a trigger point set to 5.0 g, a testing speed of 1.0 mm/s, and 2 testing cycles per sample, with each sample repeated four times to obtain the average value. A force–time curve was generated on the basis of these measurements. From this curve, hardness, elasticity, cohesiveness, and chewiness were analyzed. Six measurements were performed for each sample group.

Steaming and boiling: Chicken meatballs were weighed before (W₁) and after steaming or boiling (W₂) and cooled, and the gain–loss percentage was calculated as (_W2–W1)/W₁ × 100%.

Frying: The meatballs were weighed prefrying (G₁) and postfrying (G₂) after draining excess oil and cooling. The frying gain–loss percentage was determined via the formula (G₂ – G₁)/G₁ × 100%.

Two grams of black-bone chicken meatball samples were accurately weighed and placed into a 20 mL headspace vial. The incubation temperature was 60°C; the incubation time was 20 min; the sample volume was 500 μL; the splitless injection rate was 500 r/min; and the injection needle temperature was 85°C. Each sample group was measured in triplicate. The specific operation and parameters of the GC–IMS analysis were consistent with those of our previous paper (5). GC separation was carried out using an MXT-5 column at 60°C with high-purity nitrogen (≥99.99%) as the carrier gas over a 20-min run. The initial flow rate of 2.0 mL/min was maintained for 2 min, then increased linearly to 10 mL/min over the next 10 min, and further increased to 100 mL/min by the end of 20 min. Ion mobility spectrometry (IMS) was performed using a detector maintained at 45°C with a nitrogen flow rate of 150 mL/min, and analysis continued for 30 min. Prior to sample testing, calibration standards comprising six C4–C9 n-ketones were analyzed under identical chromatographic conditions to establish retention index (RI) versus retention time (RT) calibration curves. These ketones, with RIs set at 100 times their respective carbon numbers, were used as reference markers. VOCs in different meat cuts were identified and relatively quantified on the basis of drift time (DT) and RI values via the IMS drift time library and NIST 2010 database. The peak volume of each identified compound was also calculated to estimate its relative abundance.

All the data are presented as the means ± standard deviations (n = 3). Volatile organic compounds (VOCs) were identified via the NIST 2020 database in combination with a custom-built IMS library. Spectral differences were visually compared via the Reporter plugin, whereas quantitative differences in VOCs among samples were assessed via fingerprint analysis via the Gallery Plot plugin. Bar charts representing the relative abundances of individual components were generated via Excel 2020. Multivariate analyses, including principal component analysis (PCA) and orthogonal partial least squares-discriminant analysis (OPLS-DA), were performed via the BioDeep Tool Assistant¹, which also facilitated the creation of variable importance in projection (VIP) plots and clustering heatmaps. One-way analysis of variance (ANOVA) was conducted to assess group differences, with Duncan’s multiple range test applied for post hoc comparisons. The statistical significance was set at p < 0.05.

Sensory evaluation is the process in which evaluators use their normal visual, olfactory, and taste perception abilities to comprehensively analyze and assess the quality factors of samples, including appearance, color, and flavor (32). Compared with boiled and steamed chicken meatballs, fried black-bone chicken meatballs presented a superior color, appearance, and taste (Figure 1A). This is attributed to the Maillard reaction that occurs during air-frying, which enhances the color, flavor, and sensory characteristics of the meatballs. Although traditional deep-fat frying is considered less healthy, this study revealed that air-fried black-bone chicken meatballs presented superior sensory qualities due to reduced oil absorption. In contrast, simpler methods, such as boiling and steaming, resulted in minimal changes in texture and flavor. Given the same cooking duration, frying notably enhanced both color and flavor, which was reflected in higher sensory evaluation scores (Supplementary Table S2).

Color plays a significant role in evaluating the quality of meat and meat products and is typically evaluated through L*, a*, and b* values (10). Compared with boiled and steamed samples, the fried black-bone chicken samples presented significantly greater L*, a*, and b* values (p < 0.05) (Table 1), most likely because the Maillard reaction occurs at high temperatures during frying, and the L*a*b* values are associated primarily with the formation of brown pigments called melanoidins (29). The L* value of the boiled samples was marginally greater than that of the steamed samples, possibly because the boiling process, where the meatballs are fully submerged in water, absorbs a considerable amount of moisture, leading to a higher surface moisture content and better gloss. In contrast, steaming uses water vapor to cook meatballs, which does not impart the same level of surface gloss. The L*, a*, and b* values of the boiled and steamed samples were not different (p > 0.05), but the fried samples presented relatively high a* and b* values, indicating that frying increased the redness and yellowness of the meatball color (p < 0.05) (Figure 1A). The reasons for different colors include various external and internal factors, such as additives, proteins, myoglobin, moisture, and cooking methods, among which myoglobin primarily controls the color of raw and cooked meat (33, 34). The present air-fried meatballs might undergo the Maillard reaction at high temperatures, which significantly alters the color and aroma of the meatballs.

Texture is pivotal in evaluating food quality and consumer acceptance, providing an objective measure of meatball quality (35). The hardness, elasticity, adhesiveness, and chewiness results are shown in Figure 1. As shown in Figure 1B, the fried meatballs were significantly harder than the other groups were (p < 0.05). The hardness of the fried meatballs reached a maximum value of 840.2 g. Elasticity, which refers to the height at which the food can recover between the first bite and second bite, did not significantly differ among the groups (Figure 1C), with all values being approximately 8.5 mm. Adhesiveness quantifies the energy needed to separate semisolid foods into a swallowable form. Compared with steamed and boiled meatballs, frying increased the adhesiveness (Figure 1D) and chewiness (Figure 1E) of the black-bone chicken meatballs, reaching maximum values of 587.9 g for adhesiveness and 50.39 mJ for chewiness. These results indicate that frying can significantly improve the hardness, adhesiveness, and chewiness of black-bone chicken meatballs. Moreover, frying promotes the formation of a crispy exterior, a crucial factor in enhancing textural perception. As moisture evaporates during frying, a porous surface structure develops, while interactions between proteins and starches result in a cohesive biopolymer network. This network reinforces the crust, which fractures under chewing pressure, creating a satisfying crisp sensation. These structural modifications not only improve the mechanical attributes of the product but also increase consumer acceptance by delivering a firmer and more appealing mouthfeel (36, 37).

As shown in Figure 1F, the rate of change in the quality of black-bone chicken meatballs cooked via different methods (boiled, steamed, and fried) tended toward both loss and gain rates. The loss rate is indicated on the lower part of the horizontal axis, whereas the gain rate is represented on the upper part. For boiling, the weight of the meatballs increased. This is because the meatballs were fully immersed in water during boiling, absorbing a large amount of moisture, and when the meatballs were cooled to room temperature, the absorbed moisture had not fully evaporated, leaving some moisture inside the meatballs. During steaming, the meatballs were cooked with steam vapor. During the steaming process, some moisture entered the meatballs, but the moisture content was lower than that during boiling. The weight loss in steamed meatballs was approximately 3%, which was negligible. During frying, high temperatures cause the moisture in the meatballs to evaporate. The moisture content was significantly reduced, resulting in the greatest weight loss, approximately 9%. However, weight loss tended to be lower in fried meatballs than in boiled meatballs. This occurred because, during frying, moisture evaporated at a relatively high rate, but a crust formed on the surface of the meatballs, which effectively reduced moisture loss and enhanced the water retention ability of the meatballs. The cooking process often affects the juiciness of meat products, which in turn impacts their water-holding capacity (38). Studies on beef have demonstrated a negative correlation between juiciness and cooking loss, indicating that greater cooking losses lead to a decrease in juiciness (39).