Foods · 5 authors, 3 centres
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This study graded dried jujube (Junzao) by size and found that larger fruits had better flavor (higher sugar-acid ratio) while smaller fruits had higher antioxidant activity and mineral content. Total flavonoid content was positively correlated with antioxidant activity, and potassium was the most abundant mineral across all grades. The findings provide a reference for improving dried jujube grading standards and commercial value.
**Background:** Jujube (Ziziphus jujuba Mill.) is a nutrient-rich fruit cultivated widely in China, with Junzao accounting for approximately 37% of total dried jujube production. Dried jujube is popular for storage, transportation, and its intense flavor. Consumer purchasing decisions are heavily influenced by fruit appearance, including size and color. However, the correlation between fruit size and quality attributes of dried jujube had not been previously reported. This study aimed to understand how fruit size affects quality, antioxidant activity, mineral content, and volatile aroma components in dried jujube at the same maturity.
**Methods:** Fully matured Junzao jujubes were hand-harvested from a local farm in Xinjiang, China, and dried in a ventilated oven at 45°C for 72 hours. The dried fruits were divided into five grades (G1–G5) based on transverse diameter and number of fruits per kilogram. Quality attributes measured included shape index, moisture content, total soluble solids (TSS), total acidity (TA), sugar-acid ratio, total phenolics (TP), total flavonoids (TF), ascorbic acid (AsA), and cyclic adenosine monophosphate (cAMP). Antioxidant activity was assessed using DPPH radical scavenging and FRAP assays. Mineral elements (K, Ca, Mg, Zn, Cu) were determined by atomic absorption spectrometry. Volatile aroma components were analyzed by SPME-GC-MS. All experiments were performed with three biological and three technical replications, with statistical significance set at p < 0.05.
**Key Results:** The fruit shape index decreased from 1.66 to 1.39 as grade increased, indicating smaller fruits were more circular. Moisture content was lowest in G1 (9.2%). TSS ranged from 72.2% (G5) to 81.8%, while TA increased from 4.58 g/kg (G1) to 6.45 g/kg (G5). Sugar-acid ratios were 169.4%, 178.4%, 165.6%, 118.6%, and 111.9% for G1 through G5, respectively, with G2 having the sweetest flavor. TP content was similar across grades (8.54–9.14 g/kg), but TF increased from 2.95 g/kg (G1) to 6.14 g/kg (G5). AsA content ranged from 51.71 mg/kg to 90.80 mg/kg, peaking at G3. cAMP content peaked at G4 (363.55 mg/kg) and was lowest in G1 (210.26 mg/kg). DPPH radical scavenging activity increased with grade, with G4 showing a 7.84% increase over G3. FRAP also increased with grade, ranging from 0.43 g TE/kg (G1) upward. Potassium was the most abundant mineral, ranging from 10,223.80 mg/kg to 16,620.82 mg/kg, with G5 having the highest content. Ca content was also highest in G5, while Mg peaked in G4 (253.37 mg/kg). Zn ranged up to 4.10 mg/kg (G3) and Cu up to 3.06 mg/kg (G5). Correlation analysis showed shape index was positively correlated with TSS (R² = 0.526, p < 0.05) but negatively correlated with TA, TF, DPPH, K, Ca, Zn, and Cu. Antioxidant activity was positively correlated with TF (DPPH: R² = 0.912, p < 0.01; FRAP: R² = 0.575, p < 0.05). Twenty-nine volatile aroma components were identified, with acids (n-decanoic acid, benzoic acid, dodecanoic acid) being the most abundant. The relative content of benzoic acid reached up to 22.63% (G4), n-decanoic acid up to 16.37% (G2), and dodecanoic acid up to 18.85% (G3).
**Clinical Implications:** While this is a food science study rather than a clinical trial, the findings have nutritional relevance. Smaller and medium-sized dried jujube fruits offer higher antioxidant activity and greater mineral content (particularly potassium, which is essential for blood pressure regulation and cellular function), making them potentially more beneficial from a nutritional standpoint. The high potassium content (up to 16,620.82 mg/kg) positions dried jujube as a valuable dietary source of this mineral. The study provides evidence-based guidance for grading standards that could help consumers make informed choices based on whether they prioritize flavor (larger fruits) or nutritional density (smaller fruits). This may have implications for dietary recommendations in populations needing increased antioxidant intake or mineral supplementation.