INTRODUCTION:
Chlorophylls are bright green natural pigments found exclusively in photosynthetic plants and select bacteria. These pigments are based on a tetrapyrrole macrocycle linked by methane bridges, a stricture which is known as porphyrin. The basic structure maintains a high degree of unsaturation, providing an extended conjugated double bond system that has a high metal binding capacity. Chlorophylls are widely distributed among green fruits and vegetables. Generally chlorophyll ‘a’ predominates chlorophyll ‘b’ by a 3-to-1 margin. While native chlorophylls function mainly as primary photosynthetic pigments, their presence is considered crucial to final food product acceptance, as the green color they impart is often associated with fresh vegetable quality. Specific distribution and content of the pigments in fruits and vegetables is dependent on a number of factors including, type of vegetable, stage of maturity, growing conditions and commercial processing. (Gross, 1991)
All green plants contain chlorophyll ‘a’ and most vegetables contain both chlorophyll ‘a’ and chlorophyll ‘b’, some vegetables contain particularly high amounts of total chlorophyll.
Asparagus, bell peppers, broccoli, brussels, sprouts, green cabbage, celery, collard greens, green peas, kale, leeks, green olives, parsley, romaine lettuce, sea vegetables, spinach, swiss chard and turpin greens are concentrated sources of chlorophyll.
Consumption of green vegetables and fruits which are rich in chlorophyll has so many health benefits, where it has anti-inflammatory, antioxidant and wound healing properties. Chlorophyll and chlorophyllin are able to form tight molecular complexes with certain chemicals known or suspected to cause cancer, including poly aromatic hydrocarbons found in tobacco smoke. Chlorophyll is a good source of antioxidant nutrients such as Vitamin A, Vitamin C, and Vitamin E help to neutralize harmful molecules (free radicals) in the body that can cause damage to healthy cells. Chlorophyll and chlorophyllin may help to protect against some toxins, and may ameliorate some drug side effects.
Chlorophylls are extremely sensitive to physical and chemical changes encountered through food processing. These changes contribute to the perceivable discoloration of vegetable tissue from green to olive brown that is encountered during thermal processing and/or acidification. This color loss is predominantly a result of replacement of the centrally chelated magnesium atom by two atoms of hydrogen, producing metal free pheophytin derivatives (Schwartz and Lorenzo 1990). Retention of greenness, which is attributed by the pigment chlorophyll, is desired by consumers and processors of thermally processed green vegetables. However, the retention of chlorophyll during the cooking/processing of green vegetables has been recognized as a problem. To overcome this problem there are various techniques including alkaline salt solutions and high-temperature short time treatments. Hence the present study is carried out to identify the best cooking method among blanching, cooking with lid and cooking without lid which were normally employed in household cooking methods.
MATERIALS AND METHODS:
Chlorophyll refers to a complex of molecules (in plants and algae) that contain magnesium and basic porphrin ring structure. They are the molecules that give green pigment to plants. The function of chlorophyll in plants is to absorb sunlight, which is an essential requirement for plants to carry out photosynthesis.
The following vegetables were subjected to different cooking methods for the study entitled “Effect of cooking methods on chlorophyll content in selected vegetables”.
1. Green chillies
2. Capsicum and
3. Kovai
The study was conducted at Hyderabad and hence the selected vegetables were procured from the local vegetable market at Hyderabad. Fresh, good quality, unspoiled and optimally matured green chillies, capsicum and kovai were selected to carry out the experiment.
Preliminary processing of vegetables:
The unwanted stalls were removed manually and then washed under running tap water to remove the adhered dust and dirt present on the surface of the vegetables. After through washing, the vegetables were cut into uniform, small size pieces at length wise using stainless steel knifes. These pieces were subjected to different cooking methods and further all the samples were estimated for chlorophyll.
Cooking methods:
The following three cooking methods were used to test the cooking changes in chlorophyll content of selected vegetables.
a. Blanching
b. Cooking with lid
c. Cooking without lid
Five grams of homogeneous pieces of each vegetable samples were taken in all the cooking methods. Blanching was done for 5min, and other cooking methods were done for 10 min. Then the cooked vegetables were subjected to chlorophyll analysis.
Estimation of chlorophyll:
The AOAC procedure can be followed for the estimation of chlorophyll.
Calculation for chlorophyll percent losses:
The chlorophyll losses were calculated in comparison to the chlorophyll contents potent in the fresh vegetable as below:
Chlorophyll losses =
a =chlorophyll content in fresh vegetables
b =chlorophyll content in cooked vegetables
RESULTS:
Fresh vegetables are good sources of chlorophyll as it contain high amount of chlorophyll. Chlorophylls are widely, distributed among green fruits and vegetables, generally chlorophyll ‘a’ and chlorophyll ‘b’. The analyzed results of chlorophyll fraction in fresh and cooked with blanching, cooking with lid and cooking without lid vegetables were presented individually for each vegetable in the following manner. Table: 1
The results depicted in the table 1 showed that the total chlorophyll content in fresh green Chillies was 2.08 mg/lt. The results showed that all cooking treatments caused significant loss of chlorophyll. But compared to all cooking methods, the chlorophyll loss was les in the method cooking without lid (0.28 mg/lt) followed by blanching (0.19 mg/lt) and cooking with lid (0.10 mg/lt). Table: 2
The results in the table 2 showed that total chlorophyll content in fresh capsicum was 1.89 mg/lt, where chlorophyll ‘a’ was 0.79 mg/lt and chlorophyll ‘b’ was 1.10 mg/lt. In the all cooking methods there was a significant chlorophyll loss, but compared to all cooking methods the loss was less in cooking without lid (0.29 mg/lt) which was followed by blanching(0.14 mg/lt) and cooking with lid (0.07 mg/lt). Table: 3
The data in the table 3 showed that the fresh kovai contain 2.15 mg/lt of total chlorophyll (chlorophyll ‘a ‘was 0.87 mg/lt and chlorophyll b was 1.29 mg/lt). All the methods applied for cooking of vegetables showed significant loss in chlorophyll content. But, compared to those three methods the loss was less in the method cooking without lid (0.27mg/lt) which was followed by blanching(0.14 mg/lt) and cooking with lid (0.08 mg/lt). Table: 4
The results in the table 4 revealed that the percent losses of chlorophyll among the different vegetables subjected to various cooking methods. The loss of chlorophyll was seen in all most all vegetables under all cooking methods. Above 80% losses of chlorophyll was occur when vegetables are subjected to various cooking methods. The high percent of chlorophyll was loosed when vegetables are cooked with lid compared to other cooking methods. High percentage loss of chlorophyll was seen in kovai compared to other vegetables. Minimum losses were seen in green chillies when cooked without lid.