Walnuts Respiration (Juglans regia L) during storage

Abstract

Introduction. The respiratory rates of English walnut (Juglans Regia L.) and factors that may affect it were studied. Materials and methods. The walnut respiration intensity was determined by the confined atmosphere process. It was used the CO 2 capture method removed from the product with alkaline solution. To assess the influence of temperature on the respiration intensity of unshelled walnuts and walnut kernel, they were kept under four temperature regimes: 6±2, 18±2, 30±2 and 50±2 °C. Results and discussion. Respiration is one of the oxidoreduction processes that can lead to the oxidative degradation of walnut lipids, respectively their qualitative degradation. Walnut moisture content is one of the main factors influencing the respiratory rate. Initial respiration intensity of the walnuts is high, but falls sharply in the first 15 days of storage. This decrease being related to the reduction in walnut moisture. The respiration intensity of walnuts decreases slightly after 15 days of storage. There was established a relationship between the respiration intensity and environmental temperatures. The maximum of respiratory rates were at 30 °C. Respiration intensity of the walnut kernel is greater than that of the unshelled walnuts, the shell serving as a barrier to the direct contact between the kernel lipids and oxygen. The walnut kernel respiration intensity increaces from 5 mg to 23 CO 2 /kg•h at an increase of temperature from 5 to 30 °C. At a further increase of temperature to 60 °C the respiration intensity reduces to 15 CO 2 / kg•h. The unshelled walnut respiration intensity increaces from 5 mg to 17 CO 2 / kg•h at an increase of temperature from 5 to 30 °C. At a further increase of temperature to 60 °C the respiration intensity reduces to 12 CO 2 / kg•h. It is noted that the walnats lipids acidity index correlates with the storage temperature, but more pronounced in the case of the kernel and slower for unshelled walnuts. The acidity index of the lipids of and unshelled walnut and kernel doesn't change at an increase of temperature from 5 to 15 °C and it is approximately 0.35 mg NaOH/g prod. At a further increase of temperature to 40 °C the lipid acidity index increases to 0.8 NaOH/g prod (for the kernel) and 1.1 (for unpurified walnuts). At a further increase of temperature to 60 °C, the lipid acidity index reduces to 0.6 NaOH/g prod. Conclusions. Walnut respiration may be limited by low temperatures storage. It is therefore important to ensure storage stability by complying with the limit values for the water content of walnuts. Fruit morphologiacal state also affects the respiration intensity, this parameter being greater for kernels than for unshelled fruits, the differcence being due to shell which servs as a barrier to the direct contact between the kernel and the oxygen.

Short Cold Storage as a Sustainable Postharvest Handling Method for Natural Enrichment in Antioxidants of Fresh and Dried Walnut Kernels—Cultivar Effect

“…The initial respiration rates measured at 20 • C in 'Chandler', 'Hartley' and 'Ioli' of fresh kernels (582-1160 µmol CO 2 kg −1 h −1 ) and nuts (539-866 µmol CO 2 kg −1 h −1 ) (Table 2) were close to the range previously reported for 'Franquette' (950 and 770 µmol CO 2 kg −1 h −1 for kernels and nuts, respectively) [4]. In an unknown cultivar, respiration rates of 575 µmol CO 2 kg −1 h −1 and 425 at 30 • C for fresh kernels and nuts, respectively, have been reported [20]. The present results confirm that fresh walnuts could be classified in fruits with low to medium respiration rates [4,21].…”