Abstract
Spinach (Spinacea oleracea) is a commonly consumed plant with a high nutritional value that is rich in antioxidants but also contains high level of oxalates, which are anti-nutritive factors. In this present research four different Indian dishes were prepared from spinach: palak, plain palak saak, palak saak with ginger and palak paneer. Spices - caraway, cumin, cardamom, cinnamon, ginger and Malabathrum leaf - were added following traditional Indian recipes. The samples were collected at different stages, raw, boiled saak and saak bhaji, which were uncooked, and cooked for 15 and 25 minutes, respectively to determine the levels of total, soluble and insoluble oxalates and the antioxidant activities of spinach. High performance liquid chromatography was used to measure the total and soluble oxalate contents and an oxygen radical absorption capacity (ORAC) assay was used to measure the antioxidant activity of all spinach dishes. Initial analysis of the total, soluble and insoluble oxalate contents of the spices showed that the total oxalate contents ranged from 194 (nutmeg) to 4014 (cardamom green) mg /100 g DM, while the soluble oxalate contents ranged from 41 (nutmeg) to 3977 (cardamom) mg/100 g DM. Overall, the percentage soluble oxalate content of the spices ranged from 4.7 to 99.1% of the total oxalate content. Raw spinach contained mean total oxalate, soluble oxalate and insoluble oxalate of 7.56, 6.42 and 1.14 g/100 g DM, respectively, with a mean ratio of soluble oxalate to total oxalate of 85%. Cooking in a wok resulted in a marginal to 91% reduction in soluble oxalates due to their combination with free minerals (e.g. Ca, Fe, Mg) present in the spinach or spices. The greatest reduction (91%) of soluble oxalates occurred when paneer (a milk product) was added to the palak paneer dish; the proportion of soluble oxalate to total oxalate content was then reduced from 74-85% to 20-31%, depending on the cooking time. Spices showed ORAC values in the range of 469 (turmeric) to 794 (caraway) µmol TE/g DM. In the raw spinach dishes antioxidant activity ranged from 49 to 163 µmol TE/g DM. The antioxidant activities of cooked spinach dishes decreased from 9 to 39% depending on the ingredients added. Addition of spices showed low to moderate effects on the antioxidant activities of the cooked spinach dishes. Antioxidant activity of the palak paneer decreased in the range of 67% to 78% with the addition of paneer due to the dilution factor. This study suggested that Indian cooking styles can reduce soluble oxalate contents, where the antioxidant activity depends on the type of spices added to the dish. 1.1 Spinach in Indian diet 1 1.2 Spinach and its nutritional profile 1 1.3 Spinach and its anti-nutritional profile 1 1.4 Indian spices and herbs 2 1.5 Milk and milk products 2 1.6 Objectives of the study 3 2.1. Oxalate: An anti-nutritional component of foods 4 2.1.1 Oxalic acid and its salts 4 2.1.2 Major dietary sources of oxalates 4 2.1.3 Biosynthesis of oxalates in plants 5 2.1.4 Role of oxalates in plants 5 2.1.5 Absorption and fate of oxalate in the human body 7 2.1.6 Toxicity of oxalates in human 8 2.1.7 The effects of cooking on the oxalate levels in foods 9 2.2 Antioxidants: Nutritional components of foods 10 2.2.1 What are antioxidants? 10 2.2.2 The mechanistic functions of antioxidants 11 2.2.3 Major antioxidants found in foods 12 2.2.3 Oxygen radical absorbance capacity assay for measuring antioxidants in foods 12 2.3 Spices and associated health effects 13 3.1 Introduction 16 3.2 Method and materials 18 3.2.1 Sample material 18 3.2.2 Dry matter determination 18 3.2.3 Extraction and analysis of oxalates 18 3.2.4 High performance liquid chromatography 18 3.2.5 Statistical analysis 18 3.3 Results and Discussion 19 3.4 Conclusions 21 4.1 Introduction 22 4.2 Materials and methods 23 4.2.1 Food ingredients collection 23 4.2.2 Preparation of cooked spinach dishes 24 4.2.3 Dry matter determination 24 4.2.4 Sample extraction 24 4.2.5 High performance liquid chromatography 25 4.2.6 Analysis of proximate and minerals compositions 25 4.2.7 Calculation of standard serving size 26 4.2.8 Statistical analysis 26 4.3 Results and Discussion 26 4.4 Conclusions 35 5.1 Introduction 36 5.2 Method and materials 38 5.2.1 Food ingredients collection 38 5.2.2 Preparation of cooked spinach dishes 38 5.2.3 Sample extraction 38 5.2.4 Oxygen radical absorbance capacity assay 38 5.2.5 Calculation of standard serving size 39 5.2.6 Statistical analysis 39 5.3 Results and Discussion 39 5.4 Conclusions 45 6.0 General discussion 46
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