1. Introduction
Currently, a heightened pursuit of superior quality living has propelled consumers' expectations, particularly within the realm of food. A balanced diet and consistent physical activity are pivotal in sustaining consumer well-being [
1]. Concurrently, health hinges on the assurance of high-quality, safe food, thereby accentuating the significance of food quality. Responding to consumer preferences, numerous food producers have ventured into crafting wholesome, secure food items, prioritizing nutritional value [
2,
3]. Natural products endowed with sensory allure and heightened health merits resonate favorably with consumers [
2,
3]. Additionally, the surge in demand for functional foods, renowned for bolstering immunity and averting ailments, is evident [
4]. These functional foods wield potent health-preventive attributes, bridging the divide between pharmaceuticals and nutrition [
5,
6]. A diverse array of functional foods, including grains [
7], fruits, and vegetables, cater to consumer nutritional requisites. Fruits, being a repository of vitamins, minerals, amino acids, and bioactive compounds, constitute an indispensable facet of human sustenance [
8]. Fruit-derived antioxidant-rich compounds are renowned for curbing disease and oxidative harm [
9,
10,
11], particularly exemplified by VC, flavonoids, and phenolic compounds. Thus, the allure of antioxidant-rich foods and their processed derivatives captivates both consumers and scientific researchers [
12,
13]. Distinct fruit compositions in juices confer variable antioxidant capacity and oxygen radical scavenging prowess. Fruit juices endowed with sweet-tangy symphony potentially exhibit heightened bioactivity relative to their singular counterparts [
14,
15].
For functional fruits, medicinal edible varieties stand out, exemplified by Lycium and
C. humilis [
16,
17]. Renowned for its substantial biomass,
C. humilis emerges as a health-promoting fruit, earning monikers like "calcium fruit" and "natural calcium powder" due to its exceptional calcium content [
18]. The aromatic pulp of
C. humilis boasts remarkable nutritional value, abundant in diverse glycolic acids [
19], vitamins, mineral elements [
20], and potent antioxidant compounds [
21].
C. humilis holds significant potential across the food, nutrition, health, and medical sectors, generating considerable interest and exploration [
22], marking a recent focal point for research and utilization. Nonetheless, consumer acceptance of
C. humilis remains hindered by its inherent sourness, bitterness, and limited storability. Presently,
C. humilis has found favor in the form of processed products like dried fruit, jam, juice, and fruit wine, gaining popularity as a novel choice for calcium supplementation among the elderly and children. Regrettably, the direct consumption of
C. humilis juice proves unpalatable, necessitating the addition of numerous additives during further processing. This trajectory contrasts with consumer demand for palatable and healthful functional foods. Notably, the realm of
C. humilis juices, whether singular or mixed, remains unexplored, creating a void in
C. humilis development. To bridge this gap, we introduced high-sugar Green grape juice as an augmentation to
C. humilis juice, aiming to enhance both taste and nutritional value.
In this study, we have systematically investigated the amalgamation of C. humilis juice and Green grape juice at varying ratios, aimed at achieving an optimally palatable mixed functional juice. The interplay of bioactive constituents between these diverse juices, along with their subsequent impact on sensory attributes and physicochemical characteristics of both C. humilis and Green grape juices, encompassing color, sugar content, VC levels, antioxidant activity, and polyphenol composition, was meticulously examined both pre and post-blending. By delving into the intricacies of juice blending and the resultant alterations in bioactive constituents, this research offers valuable insights into the development of ecologically sustainable and health-enhancing juice products.
2. Materials and Methods
2.1. Experimental materials
The fruits of C. humilis No. 6 and Green grape were used as research materials. fruits of C. humilis No. 6 were provided by C. humilis planting base in Suiling County, Suihua City, Heilongjiang Province, China. Green grape was purchased from Carrefour supermarket in Lesong Square, Harbin City, Heilongjiang Province, China.
2.2. Juice production
The process of production of juice from C. humilis and Green grape involved three main technological steps:
Processing of C. humilis juice. C. humilis was ground (50% water added) in a wall breaker (L12-Energy61, Jiu Yang Co., Ltd., Shenyang, China) and then 0.02% pectinase was added to the pulp in a water bath at 50°C for 3 h. In the action of a press (Ganggu Oolong, Taobao, Changsha, China) in order to obtain the juice.
Processing of Green grape juice. During the production of juice, Green grape is ground in a wall breaker and then pressed directly with a press to obtain juice.
Juices from
C. humilis and Green grape were mixed at 34/66, 37/63, 40/60, 44/56 and 50/50 ratios immediately after obtaining. Due to the strong sour taste of
C. humilis fruits, a higher amount of Green grape juice needs to be added to the
C. humilis juice [
23].
Then, the juice products were sterilized by heating at 100°C for 5 min and placed in glass jars, pasteurized (10 min), and cooled to 20°C [
14]. Finally, seven different juices were obtained (
Table 1). Each sample was prepared in three replicates.
2.3. Consumer evaluation
The sensory assessment criteria for the processed juice in this study adhered to the guidelines outlined in the national standard "GB/T16290-1996." Evaluation of the juice products was conducted using a 10-point scale methodology, with emphasis on taste, aroma, color, and consistency attributes. A panel of 20 randomly selected consumers participated in the sensory analysis. The coded samples, presented in uniform containers, were evaluated by the panelists under controlled conditions at a temperature of 20°C [
24].
2.4. Chemical analyses
VC content was ascertained employing the method outlined by Vigneshwaran et al. [
25], based on the reaction of 2,6-dichlorophenol-indophenol with VC within the samples, under acidic conditions. An ultraviolet-visible spectrophotometer (UV-1800 model, Shimadzu, Japan) was employed to measure the absorbance at 518 nm. The quantification, presented as mg/100 ml fresh weight (FW), was carried out following established procedures. Sugars were quantified using the HPLC-ELSD technique, following the protocol delineated by Oszmianski and Lachowicz [
26]. Replicating each measurement thrice ensured accuracy. The outcomes were reported in mg/ml FW.
2.5. Colour parameters
The color attributes (L*, a*, b*) of both C. humilis and Green grape juices were assessed through reflectance measurements, employing a color spectrophotometer (CM-5, Shimadzu, Japan). The methodology outlined by Wojdyło et al. [
27] was followed for sample measurement. Measurements were conducted using a white ceramic reference plate (L* = 93.92; a* = 1.03; b* = 0.52). Each reported data point represents the mean of three separate measurements.
2.6. Total polyphenol
Total polyphenols were quantified following the Folin-Ciocalteu method as outlined by Lachowicz et al. [
28]. Briefly, samples were homogenized with distilled water and the Folin-Ciocalteu phenol reagent. The addition of a 200 g/L sodium carbonate solution ensued, inducing reaction at ambient temperature under light protection for 1 hour. Subsequently, absorbance at 765 nm was recorded using a UV-Vis spectrophotometer (UV-1800 model, Shimadzu, Japan). Total polyphenols were expressed as milligrams of gallic acid equivalent (GAE) per 100 ml FW.
2.7. Antioxidant activity
Free radical scavenging activity (DPPH)was determined following the method described by Suja et al. [
29], preparing a 0.1 mM solution of 2,2-diphenyl-1-picrylhydrazyl (DPPH) in absolute ethanol. The radical scavenging activity (%) was determined using the following formula:
(A0−A1)/A0 × 100
A0 = the absorbance of control; A1 = the absorbance of standard [
30].
The Ferric Reducing Antioxidant Power (FRAP) assay was conducted following the protocol outlined by Fu et al. [
31]. Briefly, a total of 200 μl of the extracted solution was combined with 2.8 mL of FRAP solution, comprising 0.1 M acetic acid buffer (pH = 3.6), 10 mM TPTZ, and 20 mM FeCl
3·6H
2O in a volumetric ratio of 10:1:1. The resulting sample mixture was vigorously shaken and incubated in the dark at room temperature for 10 minutes. For the blank, the extracted solution was substituted with 40% (v/v) methanol. Subsequently, the absorbance was measured at 593 nm using a spectrophotometer (UV-1800 model, Shimadzu, Japan). The FRAP results were quantified as milligrams of Trolox equivalents (TE) per 100 ml FW.
2.8. Statistical analysis
The data were analyzed using Origin 2021, SPSS, and Microsoft Excel 2020. The Student’s t-test, one-way analysis of variance, and correlation analysis were applied to detect the differences and correlations between experimental groups. A p-value of 0.05 or lower was considered to indicate statistical significance.
4. Conclusions
In this study, Green grape juice was harnessed to enhance the palatability of C. humilis juice and elucidate alterations in bioactive constituents within this functional amalgamation. The incorporation of natural Green grape juice yielded a marked enhancement in taste for C. humilis juice, concurrently minimizing reliance on artificial additives. Consumer evaluations corroborated superior scores for CG1–CG5 vis-à-vis C1, with CG5 notably securing the highest rating, attaining widespread consumer acceptance. The interplay between C. humilis juice and Green grape juice engendered discernible shifts in VC and sugar content across various blended formulations. Notably, this interaction yielded a favorable outcome, fostering an equilibrium of sour and sweet nuances that resonated more compellingly with consumers. Color attributes exhibited robust stability, manifesting a reddening trend commensurate with heightened C. humilis juice content. Remarkably, barring G1, the surveyed juices showcased commendable antioxidant activity. Particularly striking were C1 and CG5, exhibiting notable values of 850.8 mg TE/100 ml and 455.02 mg TE/100 ml, respectively. In summation, the infusion of Green grape juice emerged as a salutary practice, preserving the integrity of bioactive constituents within the juice matrix. This stratagem presents a commendable avenue to curtail the reliance on synthetic additives, facilitating the production of health-conscious, secure functional juices for discerning consumers. The pertinence of this approach extends to the food industry at large, offering applicability to diverse juice variants and promising augmented commercial value.