Innovative minimal processing of mini broccoli for keeping quality and safety and enhancing bioactive compounds

Resumen

Broccoli has shown numerous health¿promoting properties such as chemopreventive, antioxidant, antitumor, antimutagenicity, anti-inflammatory, antimicrobial, antiviral and reduction of coronary heart disease risk. The new kailan hybrid broccoli is a vegetable with remarkable more pleasant flavour and aroma than the conventional broccoli varieties, and with a bioactive and nutritive profile similar to that of broccoli and kailan. Kailan¿hybrid broccoli assembles the requirements for an excellent vegetable for the minimal processing or fresh¿cut (FC) and fifth range product industries. The kailan¿hybrid broccoli showed a significatively higher metabolic activity than that of the cv. Parthenon. Modified atmosphere packaging storage at 2 ºC (5¿7 kPa O2 + 14¿15 kPa CO2) or 5 ºC (1.5¿2.5 kPa O2 + 15¿16 kPa CO2) provides great benefits for both broccoli cvs., reaching an acceptable sensory quality and safety for consumption after 15 days of shelf¿life. The phenolic profile of both studied broccoli cvs. is similar to that reported for other B. oleracea cvs. The florets of the kailan¿hybrid broccoli showed higher total dietary fibre, protein and phenolic contents, total antioxidant capacity (TAC) and many important dietary minerals such as Ca, Mg, Fe and Zn than those of the cv. Parthenon. Emerging eco¿friendly sanitising treatments such as UV-C radiation, electrolysed water (EW) and superatmospheric oxygen have been studied in this Thesis, which may be used as potential alternatives to the conventionally used NaClO, since similar efficacy and quality retention potential were attained. In this way, low and moderate UV¿C radiation (1.5 and 4.5 kJ m¿2) retarded the natural microflora growth of FC kailan¿hybrid broccoli, keeping sensory quality for up to 19 days at 5 ºC and 13 days at 10 ºC. Moreover, the results suggest that this moderate UV¿C pretreatment could be used as a tool to increase certain health¿promoting compounds content such as polyphenols (mainly the hydroxycinnamoyl acid derivatives) and TAC. Neutral EW¿washed produce showed a potential shelf¿life of 19 days at 5ºC, as NaClO did. However, and attending to nutritional bioactive compounds, the combination of these treatments registered the highest increases of some antioxidant enzymes and achieved good fatty acids retention. Generally, there were not significant differences among double and triple combinations. The studied vacuum¿based cooking treatments generally induced better microbial, physical and sensory quality, and kept, or even improved, TAC compared to conventional cooking methods. On the other hand, grilling was one of the most effective methods to avoid undesirable changes in stem firmness, enhancing green colour, increasing total phenolic content and TAC, and reducing enterobacteria counts, even though a high visual dehydration was reached. After all cooking treatments (except grilling), an excellent microbial reduction (with mesophilic counts below 7 log CFU g¿1 after 45 days) was achieved. Based on the overall sensory quality, the commercial life was established in 45 days at 4 ºC, except for grilled (14 days) and sous vide¿treated (21 days) samples. Generally, cooking treatments induced an enrichment of health¿promoting compounds, showing MW, sous vide¿MW and LP steaming the best chlorophylls retention and total phenolic (apparently) and TAC enhancement. For those reasons, such industrial cooking methods could be recommended as a tool for keeping the quality of the fifth range kailan¿hybrid broccoli. Among the high glucosinolate content of kailan¿hybrid broccoli, glucobrassicin showed the highest levels (39 % of total glucosinolates). The innovative industrial cooking methods hereby studied on broccoli revealed that LP steaming and MW are the best ones for keeping glucosinolates and total vitamin C contents after cooking and subsequent commercial chilled storage. On the other hand, grilled samples recorded the highest losses due to the remaining myrosinase activity, indirectly registered by endogenous sulforaphane, which was undetected in the remaining cooked samples. All of the cooking treatments highly increased lutein levels, with LP steaming and MW registering the highest increases of about 7¿fold compared to uncooked samples, although a great lutein decrease was found after 14 days at 4 ºC. The kailan¿hybrid broccoli showed a great ITC absorption, which presents this new broccoli cv. as a vegetable with high potential chemopreventive properties. However, further human studies comparing this kailan¿hybrid broccoli with conventional cvs. must be conducted to corroborate this great ITC absorption. Furthermore, cooking kailan¿hybrid broccoli by MW reduced the ITC absorption in the human subjects by inactivation of myrosinase. The information hereby reported may serve as a guideline for the evaluation of potential cancer chemopreventive effects of dietary consumption of kailan¿hybrid broccoli by humans.