This research aimed to 1) develop and refine the carotenoid extraction and quantification methods for leafy green vegetables and 2) determine the effect of domestic and commercial post-harvest processing on the total carotenoid content (TCC), total phenolics content (TPC), vitamin C content, and free radical scavenging properties of spinach.

A relative response factor (RFFs) method was developed and validated for quantification of carotenoids. Using HPLC-PDA, UV spectras were documented for identification. RFFs of violaxanthin, neoxanthin, lutein, zeaxanthin, 9-cis-antheraxanthin, α-cryptoxanthin, β-cryptoxanthin, α-carotene, and lycopene were determined using β-carotene as the reference analyte. This effort overcomes the difficulty in obtaining reliable and stable carotenoid standard compounds.

A carotenoid extraction protocol using rapid saponification was developed and validated for spinach and other leafy vegetables. The method tested extraction solvent, saponification time/effects, extraction cycles, and method. The method also removed chlorophyll during extraction and solved the issue of chlorophyll coeluting with carotenoids.

Two varieties of spinach (flat leafed, savoy) were harvested from a local farm and separated into six treatments that were spinach raw, stored at 4°C for 4 days, boiled in water for 3 minutes, placed in a steam basked for 5 minutes, placed in boiling water for 30 seconds, and frozen blanched sample stored at -20°C for 30 days. The effects of processing showed an increase in TCC and a decrease in TPC, vitamin C, and free radical scavenging activity. A matrix dependent effect was seen as savoy spinach showed higher susceptibility to processing effects.

This research developed an accurate and cost-effective approach to quantify carotenoids in foods, created an accurate and efficient method of carotenoid extraction, and determined the effect of processing on spinach. This research not only provides valuable tools for the field but also helps the general population understand ways to maximize their consumption of micronutrients when eating spinach.

Xianli Wu

US Department of Agriculture

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