Harvesting times modulates the human health promoting substances in grapefruit.

Citrus fruit is grown in more than 64 countries of the world (Chaudhry et al., 2004) with a total production of 105.4 million tonnes annually (PHDEC, 2006). Citrus rank first with respect to area and production in Pakistan (Anonymous, 2013). Pakistan stands at 13th position among the citrus producing counties of the world with a total area of 199,000 acres and total annual production of 2.36 million tonnes (FAO, 2013). Citrus fruit can be divided into four main groups such as mandarins, sweet oranges, pummelo and grapefruit, and lemon and limes species. Grapefruit is ancestor of pummelo, and was separated from pummelo in 1830 (Webber, 1943). The name was given due to bearing habit just like a cluster of grapes. Shamber and Ray Ruby are the most popular pigmented grapefruit cultivars grown in Pakistan. Pakistan is characterized by a dry warm subtropical climate; making grapefruit prospers, due to its high heat requirements (Morton, 1987). It contributes important nutrients to the diet due to the presence of vitamins A, vitamin C, folic acid, potassium and dietary fiber (Mukherjee, 1997). Grapefruit is considered as preventive against cancer due to rich source of flavonoids and limonoids (Tanaka et al., 2000). It is also rich source of naringin, narirutin, and poncerin. Moreover, phytochemicals present in grapefruit act as antioxidants, anti-inflammatory, reduces the cholesterol level and modulates the immune system (Kuo, 1996). These phytochemicals in grapefruit are considered as very important for human body due to their medicinal properties . Phytochemicals constitute one of the most numerous and widely distributed groups substances in the plant kingdom. Flavonoids present in citrus fruit have been extensively studied for antioxidative, anti-cancer, antiviral, anti-inflammatory activities, capillary fragility, and inhibition of human platelet aggregation of cell during stress in body (Burns and Albrigo, 1998). Therefore, it is important that grapefruit should be harvested and consumed, when it has maximum quantity of these phytochemicals. The grapefruit produced in Pakistan are often of poor quality because growers start to harvest the fruit in early months (July and August) at immature fruit stage. At this stage, phytochemicals are not well developed, and these immature fruits are also sensitive to physiological disorders. Worldwide, efforts have been made to control these problems and to maintain the optimum quality, freshness and minimize the losses during storage (Bajwa and Anjum, 2007). A little information is available about the effects of early and delayed harvesting on these compounds. Furthermore, the harvesting time affects the accumulation of phytochemicals such as TA (total antioxidans), TC (total carotenoids), TL (total limonins), TGL (total glycoside limonins), and TPC (total phenolic contents) and TFC (total flavonoids contents) (Ahmad et al., 1992). It has been found that these phytochemicals were found in abundance at the later harvesting times in Valencia oranges (Pekmezci et al., 1995). Oliver et al. (2004) studied the effects of various Pak. J. Agri. Sci., Vol. 52(2), 393-401; 2015 ISSN (Print) 0552-9034, ISSN (Online) 2076-0906 http://www.pakjas. com.pk