Evaluation of fining agents for clarification of kinnow mandarin juice

Introduction

Citrus (Citrus spp.) belongs to the family Rutaceae. These fruits are immensely popular worldwide for their flavour and nutrition. Citrus originated in South East Asia and is now grown in tropical-subtropical belt from 40° latitude North to 40° latitude South, in both humid and arid regions. Citrus has an important place in world fruit production (Cooper and Chapot, 1977) [2] . Plants in this genus produce citrus fruits, which includes important crops such as orange, mandarin, lemon, lime and tangerines. Among the citrus group, Kinnow is a high yielding mandarin hybrid cultivated extensively in Punjab, Haryana and Rajasthan in India and also the main horticulture crop of Pakistani Punjab. Kinnow mandarin is a hybrid between C. nobilis and C. deliciosa. The fruit has distinct aroma and flavour, which makes it highly suitable for table fruit and for processing (Ilame and Singh, 2018) [4] . Fruit juices are widely consumed beverages valued for their nutritional and healthpromoting properties, containing essential bioactive compounds such as flavonoids, carotenoids, vitamins, minerals, and polyphenols that help prevent chronic diseases and support overall well-being (Ahmed et al., 2018) [1] . Kinnow juice is a rich source of vitamin C and various antioxidant compounds that are required to sustain healthy life. It is also a rich source of primary metabolites such as amino acid, vitamins (ascorbic acid, provitamin-A, and folate) as well as secondary metabolites. However, the presence of suspended particulate matter reduces their clarity, quality, and consumer acceptability. Clarification is therefore a crucial step in juice processing, ensuring stability, visual appeal, flavor enhancement, and extended shelf life. Various clarifying methods such as microfiltration, enzymatic treatment, and fining agents including gelatin, bentonite, activated carbon, silica gel, and albumin are employed to remove proteins, phenolics, and other colloidal substances (Deshmukh, K.Y). Protein-based agents like gelatin and albumin bind with tannins and proteins, while bentonite and colloidal silica effectively eliminate proteins, preventing haze formation. Application of fining agents improves clarity, enhances consumer acceptance, and prolongs storage stability, making the process pivotal for fruit juice industry sustainability and marketability. Kinnow mandarin juice, though nutritionally rich, is often turbid due to suspended particles and colloidal substances, which lower its consumer acceptability and market value. Clarification using fining agents improves clarity, colour, and stability by removing hazeforming compounds, thereby enhancing sensory qualities, shelf life, and overall marketability of the juice. Hence, the present study was carried out to develop a high-quality, stable, and consumer-acceptable kinnow mandarin juice through clarification using suitable fining agents.

Material and methods

The research was carried out in the Postharvest Management Laboratory at the College of Horticulture, Anantharajupeta, Annamayya district, Andhra Pradesh. The following methodology was followed for the preparation of Kinnow mandarin juice and the steps are described below:

Selection of fruits

Fresh, fully ripened and high-quality kinnow mandarin fruits were selected and procured from the local market at Railway kodur. The fruits were sorted to eliminate any damaged or spoiled ones. After sorting, the selected fruits were washed and peeled to remove any impurities.

Preparation of Kinnow mandarin juice

The peeled fruits were sliced into pieces for processing. Clear juice extracted by separating the pulp and seeds using the Hurrom H-100 juicer. The obtained juice was filtered to remove minor impurities and sodium benzoate was added as a preservative to extend the shelf life. 2% of different fining agents were added and the juice was pasteurized at 85 °C for 1 min. The pasteurized juice was immediately cooled and stored at 3°C to 5°C for further use.

Filling, Bottling and capping

The prepared juice was filled into glass bottles according to the treatments and replications, followed by capping and stored at room temperature for 15 days to conduct storage experiments. [7] . Total soluble solids, expressed in °Brix, were measured using an Atago RX1000 digital refractometer (HRN-18). Titratable acidity was estimated using a titration method with NaOH as the neutralizer and phenolphthalein as the indicator for endpoint detection. Ascorbic acid content was estimated by using the 2,6-dichlorophenol indophenol titration technique described by Sadasivam and Manickam (1992). Juice clarity was measured according to the methods of Krop and Pilnik (1974) [6] and Ough and Crowell (1979) [8] .

Results and discussion

Data related to physico -chemical parameters which include pH, total soluble solids, were presented in Table 1 and titratable acidity, ascorbic acid were detailed in Table 2.

Clarity were detailed in Table 3 during 15 days of storage at 5 days interval.

pH

The pH of clarified kinnow mandarin juice was declined during storage. T2 (2% Gelatin) shows the minimum pH followed by T 1 (2% Bentonite). The maximum pH was recorded in T 7 (Without fining agent at ambient temperature -control) which is on par with T 6 (Without fining agent at refrigerated (4°C) condition) during the 15 days of storage. The similar findings were observed in Jafari et al., (2024) [5] in Indian gooseberry juice.

TSS (°Brix)

With regard to TSS of kinnow mandarin clarified juice, a gradual decline was observed during storage. The maximum TSS was recorded in T 7 (Without fining agent at ambient temperature -control), while the minimum was observed in T 2 (2% gelatin). A similar trend continued throughout the 15 days of storage. The results aligned with the findings of Jafari et al., (2024) [5] in Indian gooseberry juice. Similar results were reported by Taştan and Baysal (2017) [9] in apple juice.

The titratable acidity of clarified kinnow mandarin juice showed a gradual increase during storage. The percentage of titratable acidity, significantly highest acidity of was found in T 2 (2% Gelatin) followed by T 1 (2% Bentonite). Lowest acidity of was found in T 7 (Without fining agent at ambient temperature -control). Similar findings were recorded in Jafari et al., (2024) [5] in Indian gooseberry juice.

Regarding the percentage of ascorbic acid, significantly highest was found in T 2 (2% Gelatin) followed by T 1 (2% Bentonite). Lowest was found in T 7 . The ascorbic acid of clarified kinnow mandarin juice showed a gradual increase during storage. A similar trend continued throughout the 15 days of storage, with T 2 (2% Gelatin) consistently exhibiting the highest ascorbic acid (31.00, 31.09, 31.17 and 31.22 at 0, 5, 10, and 15 DAS, respectively), followed by T 1 (2% Bentonie). In contrast, T 7 (Without fining agent at ambient temperature -control) maintained the lowest ascorbic acid (21.50, 21.60, 21.65 and 21.71) at 0, 5, 10, and 15 DAS, respectively. The results aligned with the findings of Jafari et al., (2024) [5] in Indian gooseberry juice. [5] in Indian gooseberry juice.

Conclusion

The present study concluded that the use of 2% gelatin significantly improved the clarity and physicochemical quality of kinnow mandarin juice. These findings provide valuable insights for the large-scale production of highquality clarified juices, which can be further utilized in the preparation of value-added products.

Acknowledgement

AcknowledgementI would like to express my heartfelt gratitude to my chairperson, Dr. C.N. Byanna, Co-chairperson Dr. M. Siva Prasad and Dr. Ch. Ruth for their invaluable support throughout this research work. I also extend my thanks to the Department of Postharvest Management, College of Horticulture, Anantharajupeta, for providing essential resources and to my family and friends for their unwavering encouragement.

References

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