In the present study, the effects of three production processes (pressing of roasted pumpkin seed paste, pressing of unroasted ground pumpkin seeds and pressing of unroasted ground pumpkin seeds while cooling the press) on the properties of pumpkin seed oils produced from two seed varieties (husked and naked) were investigated. Oils produced with roasting had a higher initial peroxide value (PV), twofold higher total phenol content and better oxidative stability while cold pressed oils had higher tocopherol content. Fatty acid and triacylglycerol compositions were not significantly affected by the processing conditions. Oxidative stability of the oils positively correlated with oleic acid content and negatively correlated with linoleic and linolenic acid contents. The lack of correlation in oxidative stability with tocopherol and polyphenol contents suggests that improvement in oxidative stability of roasted oils could have been caused by antioxidative Maillard reaction products or inactivation of oil degrading enzymes. In addition, oils produced from husked seeds had significantly higher linoleic acid, triacylglycerols (TAG) containing mainly linoleic acid (LLL, OLL and PLL), tocopherol and phenol contents while oleic acid and TAG containing mainly oleic acid (LOO and OOO) contents and oxidative stability were lower. Principal component analysis (PCA) of the analytical data confirmed the observed differences between oils from two varieties and three production processes.

Conditioning rapeseed can significantly increase the amount of bioactive compounds in the crude oil, but if the conditioning temperatures are too high, they can cause unwanted side effects such as darker color and sensory defects. Modest conditioning temperatures may be more suitable, but little is known about the effects on the quality and bioactive composition of the resulting oil. Oil was recovered from five rapeseed cultivars by cold pressing (CP) or by pressing seeds conditioned at 80 °C for 30 min (HP). Conditioning rapeseed increased oil yield without changing fatty acid composition and increased the amount of total sterols by 16 %, total tocopherols by 20 %, and the levels of polyphenols. Levels of the polyphenol canolol were up to 55‐fold higher in HP oil than in CP oil. These higher levels of bioactive compounds gave HP oil higher radical scavenging activity. Although HP oil also had higher free fatty acid contents, peroxide levels, and specific UV extinctions (K values). The quality parameters of HP and CP oils were within codex limits indicating high quality. Modest conditioning temperatures can be used to produce rapeseed oil with high quality and radical scavenging activity.

SUMMARY Heating the rapeseed prior to the oil extraction is conducted to increase the oil yield but it can also induce changes of various components of the seed. These changes may affect the composition of the volatile and non-volatile compounds of produced virgin rapeseed oil. The aim of our study is to determine the impact of different conditioning temperatures (60, 80 and 100 °C) on the quality, nutritional value, aroma profile and sensory characteristics of virgin rapeseed oil. Conditioning the seeds at all three temperatures had no influence on the quality and major nutritional components (fatty acids and tocopherols) of the produced oil. However, temperature increase caused an exponential increase of canolol and significant changes in the aroma and sensory profile of the produced oil samples. The dominant volatile compounds of cold-pressed and virgin oil produced at 60 °C were enzymatic degradation products of glucosinolates (isothiocyanates and epithionitriles), responsible for pronounced seed-like flavour of these types of oil. Increasing production temperature deactivated enzymes and caused thermal decomposition of seed components and increment of nitriles, aldehydes, pyrazines and furanes, carriers of nutty and roasty flavour. These results can help producers to design virgin rapeseed oil with specific and desirable sensory characteristics.

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