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LWT - Food Science and Technology 42 (2009) 50–55
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Bitterness, odor properties and volatile compounds of virgin olive oil with phospholipids addition O. Koprivnjak a, *, D. Sˇkevin b, S. Petricˇevic´ c, K. Brkic´ Bubola d, Zˇ. Mokrovcˇak b a
Department of Food Technology & Control, School of Medicine, University of Rijeka, Brac´e Branchetta 20, 51000 Rijeka, Croatia Department of Food Technological Engineering, Faculty of Food Technology and Biotechnology, Pierottijeva 6, 10000 Zagreb, Croatia c sms Food Development Centre, Kurtovic´i bb, 23231 Klis, Croatia d Institute of Agriculture and Tourism, K. Huguesa 8, 52440 Porecˇ, Croatia b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 January 2008 Received in revised form 31 March 2008 Accepted 8 May 2008
Bitter hydrophilic phenolic compounds contained in virgin olive oil (VOO) beneficially affect human health. However, consumers mostly do not tolerate oils with a pronounced bitter taste (bitterness index K225 0.360) and this could limit their consumption. The possibility of bitterness attenuation of quite bitter VOO (K225 ¼ 0.501) by the addition of granular soy lecithin, as a source of phospholipids, up to the levels present in seed oils (2.5–30 g/kg), was evaluated by sensory difference tests. Statistically significant differences were found starting from 5 g/kg of added phospholipids (p 0.05). Phospholipids addition caused a significant decrease of the total concentration of 20 volatiles determined by HS-SPME–GC analysis (slope 0.056; r ¼ 0.9962), and the most influenced among them was E-2-hexenal (slope 0.048; r ¼ 0.9975). Results of quantitative descriptive sensory analysis showed that the addition of phospholipids in a range from 5 to 10 g/kg slightly reduced olive fruity and green odor notes, significantly increased sweetness and decreased bitterness. The significant changes of overall sensory quality grading were not found between pure VOO and samples enriched with phospholipids. Thus, in the context of functional food formulation, addition of phospholipids could be proposed as a procedure useful for bitterness attenuation of VOO. Ó 2008 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved.
Keywords: Olive oil Phospholipids Bitterness Volatiles Odor properties
1. Introduction Chemopreventive phytonutrients are naturally occurring ingredients of plant foods that beneficially affect human health. Many efforts in plant production and food processing are directed to enhance or preserve existing phytonutrients, as well as to create functional foods by their addition to the significant concentration levels. However, a lot of known phytonutrients, such as phenolic compounds, flavonoids, terpenes and glucosinolates, are bitter or astringent (Drewnowski & Gomez-Carneros, 2000). This imposes limitations in enrichment possibilities, because the consumers mostly do not tolerate pronounced bitter taste of food. The main phenolic compounds responsible for the bitter taste of virgin olive oils are secoiridoids, hydrophilic aglycone derivatives of oleuropein and ligstroside. Among them, the major contribution has aldehydic form of oleuropein aglycone (Mateos, Cert, PerezCamino, & Garcia, 2004), although high correlation coefficients between oil bitterness and the concentration of total phenols have also been reported (Morales & Tsimidou, 2000). Their health
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[email protected] (O. Koprivnjak).
beneficial effects are related to the prevention of cardiovascular diseases, cancer and neuro-degenerative diseases (Servili et al., 2004; Visioli, Galli, Galli, & Caruso, 2002). These impacts are primarily attributed to their antioxidant activity in vivo, but some other pharmacological effects, such as inhibition of cyclooxygenases, have also been reported (Yang, Kong, & Zhang, 2007). Despite these positive aspects, consumers prefer virgin olive oils with low or moderate levels of bitterness, rejecting very bitter ones (Mateos et al., 2004). In order to improve the acceptance of bitter food or drugs, different bitter-taste masking substances have been studied, e.g. sugars (Kreutzmann, Christensen, & Edelenbos, 2008), sweeteners, sodium ions, adenosine monophosphate, cyclodextrins (Binello, Cravotto, Nano, & Spagliardi, 2004), flavanones, hydroxybenzoic acid vanillylamides (Ley, Blings, Paetz, Krammer, & Bertram, 2006), lipoproteins and phosphatidic acid (Katsuragi et al., 1997). In most cases, bitterness-masking potential has been evaluated in aqueous solutions of different standard bitter substances, such as caffeine, quinine, propylthiouracil, and bitter peptides. Little information exists about bitter-taste masking substances applied to model systems or real food matrixes. As regards olive oil phenols, Pripp, Busch, and Vreeker (2004) studied the effect of sodium caseinate on bitterness of 65% oil in water emulsion. They have found that the
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O. Koprivnjak et al. / LWT - Food Science and Technology 42 (2009) 50–55
addition of 1% of sodium caseinate significantly reduce the bitterness of emulsion containing phenols extracted from virgin olive oil, despite relatively weak binding of these phenols to proteins. According to our knowledge, the addition of bitterness-masking substances directly to virgin olive oils has not been reported yet. It must be noticed that no additives are permitted in virgin olive oils (Codex Alimentarius, 1981), so in case a bitterness-masking substance is used, the resulting olive oil is not be considered virgin, but it could be interesting as a particular functional food formula. Katsuragi et al. (1997) have proposed phospholipids (PL), i.e. lecithin fractions with a high content of the phosphatidylinositol and phosphatidic acid, as a bitterness inhibitor for practical applications. They have demonstrated that these fractions sufficiently inhibit the bitterness of many bitter substances, when they are dissolved together in water solutions, incorporated to the granules or used as coating of the granules containing bitter substances. Phospholipids are one of the minor constituents of seed oils, in which they are usually present in concentration range from 10 to 20 g/kg (Bernardini, 1983). Virgin olive oils contain amounts of phospholipids that are 300–400 times lower than in seed oils (Koidis & Boskou, 2006). Thus, VOO could be a suitable matrix for addition of those possible bitterness inhibitors. In this work we investigated the possibility of bitterness attenuation of extra virgin olive oil with pronounced bitter taste, by addition of granular soy lecithin as the source of PL. To select the appropriate concentration range of PL and to verify its influence on the perception of bitter taste, sensory difference tests were applied. Besides, the effect of the increased PL concentration on odor properties was evaluated by quantitative descriptive analysis and correlated to the concentration changes of volatile substances, determined by GC analysis of oil headspace volatile composition after solid-phase microextraction (SPME). 2. Materials and methods 2.1. Materials A filtered extra VOO was purchased from a local Croatian olive oil producer. De-oiled soy lecithin in the form of granules around 2 mm in diameter, characterized by neutral taste and moderately expressed odor reminding dry soybeans, was supplied from Life Time Nutritional Specialities Inc. (Anaheim, USA). It contained 30 g/ kg of phosphorus, 37 g/kg of choline, 22 g/kg of inositol,