spoon

 

New Zealand

 

A Cracker of a Nut

Nutritional Gem

G.P. SAVAGE
Food Group, AFSD, Lincoln University, Canterbury

Presented to the NZ Walnut Industry Group Research Field Day, Saturday 2nd March, 2002

Summary

Walnuts contain between 52 and 70% oil. More than 90% of this oil contains unsaturated fatty acids, and the oleic acid (a monounsaturated fatty acid) content ranges from 12 to 20%. Phytosterols and vitamin E are also dissolved in the oil fraction and these, along with oleic acid, are the most positive nutritional features of walnuts.

Some nutrition experiments have shown the potential cholesterol lowering effect of consuming walnuts but they seldom record the full nutritional profile of the nuts. New Zealand grown cultivars show a wide content range of these important constituents. Nuts may protect against coronary heart disease through a number of mechanisms. Walnuts contain about 10% linolenic acid, which has been associated with reduced risk in several prospective studiesa, possibly due to antithrombotica and antiarrhymica effects of -linolenic acid. Walnuts are an excellent source of protein, the crude protein content of New Zealand walnuts ranges from 13.6 to 18.1 g crude protein/100 g DM. Walnuts are rich in arginine, a precursor of nitric oxide, a potent vasodilator, which can inhibit platelet adhesion and aggregation. Other suggested benefits of nuts include their high content of magnesium, copper, folic acid, protein, potassium, fibre and vitamin E.

The complete composition of walnuts grown in different parts of the world has not been fully described. New Zealand grown walnuts have distinctive nutritional profiles and some cultivars may prove to have a greater positive metabolic effect than other cultivars.

Analysis has shown that Rex, a New Zealand selected walnut, contained the highest level of polyunsaturated fatty acids of any cultivar. Initial analysis showed that feeding the cultivar Rex as a dietary supplement had a positive effect on the blood profile lowering the levels of cholesterol, LDL-cholesterol and triglycerides of most of the volunteers. It is likely that this effect was caused by the addition of polyunsaturated fatty acids, plant sterols and vitamin E from the nuts. The additional dietary fibre found in the nuts should also not be overlooked. Overall these results confirm that walnuts are a healthy addition to the diet.