Characteristics of raspberry (Rubus idaeus L.) seed oil

Abstract

Studies were conducted on properties of oil extracted from raspberry seeds. Oil yield from the seed was 10.7%. Physicochemical properties of the oil include: saponification number 191; diene value 0.837; p-anisidine value 14.3; peroxide value 8.25 meq/kg; carotenoid content 23 mg/100 g; and viscosity of 26 mPa.s at 25°C. Raspberry seed oil showed absorbance in the UV-B and UV-C ranges with potential for use as a broad spectrum UV protectant. The seed oil was rich in tocopherols with the following composition (mg/100 g): α-tocopherol 71; γ-tocopherol 272; δ-tocopherol 17.4; and total vitamin E equivalent of 97. The oil had good oxidation resistance and storage stability. Lipid fractionation of crude raspberry seed oil yielded 93.7% neutral lipids, 3.5% phospholipids, and 2.7% free fatty acids. The main fatty acids of crude oil were C18:2 n-6 (54.5%), C18:3 n-3 (29.1%), C18:1 n-9 (12.0%), and C16:0 (2.7%). The ratio of fatty acids, polyunsaturates to monounsaturates to saturates varied depending on lipid fraction. Polymorphic changes were observed in thermal properties of raspberry seed oil.

Introduction

About 18,000 metric tonnes of raspberries are produced annually in Canada with the total global production at 312 thousand metric tonnes. In the processing of raspberry juice, the seed becomes a byproduct which is currently under exploited. Oil from raspberry seed could amount to over 400 metric tonnes, assuming 10% of seed in fresh berries, 23% oil content of seeds (Johansson, Laakso & Kallio, 1997) and that all raspberry produced in Canada is processed as juice.

The composition of raspberry seeds compiled by Winton and Winton (1935) reveals that as early as 1907 oil expressed from the seed amounted to 14.6–18%. These raspberry seed oils contained 0.73–1.10% phytosterol, and had a saponification value of 187–192. Recently, Johansson et al. (1997) found that linoleic, α-linolenic, oleic and palmitic acids were typically the most abundant fatty acids from seed oil of 22 common edible wild northern berries, including raspberry. The seed mass, 100 seed weight, and seed oil content for raspberry were 10.1% (fw), 180 mg, and 23.2%, respectively.

Storage studies by Carnat, Pourrat and Pourrat (1979) showed that raspberry seed oil oxidized very slowly even at 60°C with an increase in peroxide value from 3 to 39 mmol/kg over 7 days. At ambient temperature (22–23°C), oxidation was slower yet, with peroxide values varying from 3 to 18 mmol/kg after 5 weeks. This resistance to oxidation of raspberry seed oil was purported to be due to the presence of a minor component in the unsaponifiable fraction of the oil (Carnat et al.). In the quest to understand the oxidative stability of raspberry seed oil, Pourrat and Carnat (1981) stabilized the moisture content of raspberry seed to 5–6% by drying at 50°C for 4–5 h, then extracted oil with chloroform. The oil yield was 16–18% by that process and the fatty acid composition in percentage of the chloroform extracted oil was: C16:0, 2.7; C18:0, 0.2; C18:1, 18.7; C18:2, 55.5; and C18:3, 32.6 (Pourrat & Carnat, 1981). The definitive reason for the high stability of raspberry seed oil has not been fully clarified.

The incorporation of raspberry seed oil in cosmetics and pharmaceutical products based on its anti-inflammatory activity notably for the prevention of gingivitis, rash, eczema, and other skin lesions has been patented (Pourrat & Pourrat). The anti-inflammatory activity of raspberry seed oil was superior compared to those of other well-known oils such as virgin avocado oil, grapeseed oil, hazelnut oil, and wheat germ oil (Pourrat & Pourrat). According to this patent, raspberry seed oil can be used as a sun screen, in toothpaste, cremes for prevention of skin irritations, bath oil, aftershave cream, antiperspirants, shampoos, and lipsticks.

Red raspberry forms part of the Pacific Agri-Food Research Centre small fruit breeding program. In addition to the release of new cultivars with high yields of large fruits with excellent quality, pleasant flavor, firm fruit and low susceptibility to pre- and postharvest diseases, there is interest in the complete utilization of the fruit for food and non-food uses. Raspberry seed oil may be regarded as a speciality oil and as such may attract considerable attention because of its possible nutraceutical effects. It is a rare commodity and currently retails at $52 a litre as a fragrant oil. Our aim is to transform raspberry seed into economically valuable ingredients for the food and nonfood industries. In this context, the chemical and physical properties of oil extracted from raspberry seed has been investigated to provide guidelines for innovative uses of this byproduct. The properties of raspberry seed oil was also compared with those of two commercial oils, grapeseed and safflower oils used in the food, cosmetic and pharmaceutical industries.