Influence of refrigerated adsorption dehumidified drying towards the retention of phenolic, flavonoid and antioxidant properties of small cardamom (Elettaria cardamomum): Performance comparison with convection, solar and fluidized bed dryer
Introduction
Spices are known for their aroma and flavour and are an essential ingredient in the preparation of a wide range of cuisine across the globe. Spices contain a wide range of antioxidants, most of which directly or indirectly aid in metabolism, growth and development among humans (Mishra et al., 2021). Besides food and related applications, essential oils and dried powders obtained from various spices are increasingly used in different industries such as food, pharmaceutical and cosmetic industries, since similar synthetic compounds are higher in cost and have health concerns (Moure et al., 2001).
Cardamom is one of the most widely and actively used spices and is generally used in the form of dried cardamom, powders and also oil. The main components in cardamom oil include 1,8-cineole, α-terpinyl acetate, and limonene, which account for two-thirds of total volatiles. Besides, cardamom oil also contains myrcene, methyl heptenone, pinene, linalool acetate and other compounds which are used widely as anti-bacterial, anti-oxidant, anti-inflammatory, and anti-ulcerogenic agents (Ashokkumar et al., 2020).
The most important step in the manufacturing of any dried spices, particularly cardamom is drying. Fresh cardamom usually has a moisture content of around 80% (in wet basis) and hence has a minimal shelf life of 2 days (Balakrishnan et al., 2011). In order to process cardamom and extract the bioactives or essential oil, drying is an inevitable requirement. It is critically important to dry the cardamom capsules as soon as it is harvested to prevent degradation, flavour & colour loss, quality and loss of bioactives.
Traditionally, either solar drying or HACD are widely used for the drying of wide range of spices, including cardamom capsules. However, drying via direct solar drying or HACD are associated with anti-oxidant losses, phenolic and flavonoid losses since there is no control over temperature in solar drying or HACD (Shreelavaniya et al., 2016 Jeevarathinam et al., 2021). Temperature plays a critical role in oil yield and oil yield of cardamom decrease significantly with increase in drying temperature (Wang et al., 2021). Lakshmi et al. (2018) developed a mixed mode hybrid solar dryer with integrated thermal energy systems for drying of black pepper and found that the developed model helped in better retention of antioxidants. Omanakutty and Joy (2007) in their study proved that the process of cold grinding enhances the volatile oil content and the quality of the oil in terms of its aromatic constituents. Hence, advances in drying methods like heat pump dryers, pre-treatments and hybrid drying are being explored to retain the bioactives from cardamom (Athira et al., 2022; Pandiselvam et al., 2022, Pandiselvam et al., 2022).
There are reports on usage of advanced drying methods for spices, especially cardamom which discusses the drying efficiency, drying kinetics and its energy comparison. However, reports or literature which specially discuss the performance of various dryers in terms of bioactive retention for spices is not available. Under this context, this paper discusses the performance of RADD, which is custom-made and developed by CSIR-NIIST, Thiruvananthapuram for drying of green cardamom. The main objective behind the developed model was to reduce the humidity inside drying chamber which will result in greater mass transfer rate from the spices like nutmeg and cardamom during the process of drying. Once the drying is completed, hot humid air from the drying chamber is passed inside a refrigeration system again via finned tube heat exchangers for energy efficiency. In the refrigeration system (which works on rankine cycle), refrigerant absorbs the sensible heat and latent heat of condensation from the partially-cooled humid air to cool it below its dew point. In the meantime, refrigerant leaving the evaporator is compressed and the heat of compression is removed in the condenser after exchanging heat with the recycled air stream to heat the dehumidified air, which is used in the drying chamber and the cycle continues. The schematic representation of RADD and its specifications along with other dryers used in the study was given in supplementary file.
Conventional HACD and STD are getting replaced by FBD to ensure enhanced drying rates and performance. However, drying in FBD is associated with antioxidant losses and other bioactives due to higher drying rates, this study is aimed at the suitability of RADD over FBD and other conventional dryers in terms of drying efficiency, retention of colour and essential oil yield. Considering the importance and need for drying cardamom for shelf life enhancement, it becomes necessary to ensure the bioactive, aroma and colour retention of cardamom during drying operation. However, the drawbacks of FBD like loss of bioactives etc., can be eliminated by use of RADD. Under this perspective, this paper critically evaluates the end property attributes of RADD and the values are compared with FBD as well as conventional drying methods.
Section snippets
Materials
Cardamom samples of variety Njallani green gold were procured from Kumily village, Idukki, Kerala, India, and the same variety was used throughout the study. All chemicals and standards used for the study were of analytical grade with high purity. Standard Galic acid (≥98.0%), and standard Quercetin (≥95%) were purchased from Merck KGaA (Sigma-Aldrich), Darmstadt, Germany. Folin & Ciocalteu's Phenol reagent and methanol were purchased from Sisco Research Laboratories Pvt. Ltd., Maharashtra,
Colour
Drying significantly affects the colour due to prolonged exposure to heat. For fresh cardamom, the values of L* , a* , and b* values were found to be 37.06 ± 1.853, (−3.71) ± 0.185, 25.25 ± 1.262 respectively. During the drying operation of solar drying and other conventional sun drying operations, there is a considerable change in colour due to degradation of colour pigments like chlorophyll via continuous exposure to heat and oxidation (air) (Shreelavaniya et al., 2021).
Total colour change is
Conclusion
Cardamom were dried using 4 different dryers, of which two of them ie, HACD and STD dryer were conventional dryers and the third one was FBD and the last one is RADD which employed a low humid air. Retention of phenolic compounds, flavonoids, antioxidant, oil yield, and essential oil composition was determined for cardamom samples dried in all four dryers. The study proved that compared to other modes of drying, RADD is found to have better retention of bioactives, since air was dehumidified to
Funding
The author Venkatesh T, would like to thank the Department of Science and Technology, Government of India, for their funding via the project number SP/YO/2019/1496. Author, Muthu Arumugam would like to thank DBT, Govt of India through project No. BT/PR14219/AAQ/3/ 740/2015 for their GC-MS instrumental facility.
CRediT authorship contribution statement
Silpa V – Writing – original draft, Data curation, Formal analysis, Investigation. Athira V A - Writing – review & editing, Formal analysis, Investigation.Nandhulal A M – Performing Experiments, Data curation. Gokulvel E - Performing Experiments, Data curation. Tripti Mishra: Writing – review & editing, Validation (GC-MS). Venugopalan V V: – Supervision, Project administration. Muthu Arumugam: Validation (GC-MS). Anjineyulu Kothakota: Supervision. Venkatesh T: Writing – review & editing,
Declaration of Competing Interest
The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:Venkatesh T reports financial support was provided by DST INDIA.
Acknowledgement
Corresponding author would like to acknowledge Dr. Reshma M V, Principal Scientist and Mr. Venugopalan V V, Senior Principal Scientist for their guidance and support throughout his scientific career.
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