Abstract
Lettuce (Lactuca sativa) was grown using a foliar spray with whey protein hydrolysate (WPH) as opposed to normal nitrate fertilization. Lettuce juice was prepared from lettuce cultivated without any fertilization, nitrate fertilization, or WPH. Sixty weaned, 4-week-old male V-line rabbits with an average 455 ± 6 g body weight were randomly divided into 4 groups (n = 15) and administered different lettuce juices. Rabbits administered WPH-fertilized lettuce showed significantly higher (n = 5, p < 0.05) body weight and carcass weight than those receiving nitrate-fertilized lettuce. Rabbits administered nitrate-fertilized lettuce were associated with significantly (p < 0.05) higher levels of liver enzyme activities (AST, ALT, and ALP), bilirubin (total, direct, and indirect), and kidney biomarkers (creatinine, urea, and uric acid). Rabbits administered WPH-fertilized lettuce avoided such increases and exhibited normal levels of serum proteins. Rabbits administered nitrate-fertilized lettuce manifested significantly (p < 0.05) lower RBCs and Hb levels than that of the other groups, while those receiving WPH-fertilized lettuce showed the highest levels. Liver and kidney sections of rabbits receiving WPH-fertilized lettuce witnessed the absence of the histopathological changes induced by feeding on nitrate-fertilized lettuce and produced higher quality meat. WPH-lettuce can substitute nitrate-fertilized lettuce in feeding rabbits for better performance and health aspects.
Highlights
Attention is increasingly paid to the accumulation of nitrate in vegetables over fears of its adverse effect on human health
The results revealed that nitrate-rich lettuce administration to female rabbits caused a reduction in the hemoglobin concentration in the blood, probably due to increased activity of the endothelial heme oxygenase by nitric oxide, degrading heme to carbon monoxide and biliverdin [42]
Rabbits administered whey protein hydrolysate (WPH)-fertilized lettuce could maintain significantly increased body weight during the whole rearing period, overcoming the observed reduction induced by feeding on nitrate-fertilized lettuce
Summary
Attention is increasingly paid to the accumulation of nitrate in vegetables over fears of its adverse effect on human health. After entering the human body, bacteria and certain enzymes present in the human digestive system may convert nitrate to nitrite, which reaches the blood system where it oxidizes Fe2+ into Fe3+. Biomolecules 2021, 11, 835 compounds [1]. About 72–94% of the total nitrate N is supplied to humans with daily vegetable diets [2]. For these reasons, many countries set up nitrate concentration limits for vegetables. In 1997, the European Union officially established maximum limits for nitrate in some vegetables, such as spinach and lettuce [3]. In China, Shen et al [4] proposed
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