TIME AND TEMPERATURE OF THE INITIAL HEATING STEP OF HOT-BREAK PROCESSING REQUIRED FOR ENHANCING LYCOPENE DIFFUSIVITY OF TOMATO PUREES

Tomato is known as being one of the main sources of carotenoid for human diet. Carotenoids contained in tomatoes are mainly lycopene, and, at a much lower level, β-carotene and lutein. All of them have been extensively identified as being beneficial to human health, even if a large part of their mode of action remain unexplained. On the side of the food research, a large effort is devoted to explain their bioaccessibility, i.e., the real proportion available for absorption by the digestive tract. It has been indeed shown that only a little proportion of the ingested carotenoids is liberated from the food matrix and reaches the mixed micelles, i.e., the form in which they are absorbed by the gut cells. Numerous factors were identified as potentially limiting this transfer (West & Castenmiller, 1998), some being attributed to food matrix properties.
Biophysical barrier exists in tomato for the diffusion of lycopene to oil, as occurred in the first part of the digestion. Even in non-saturating conditions (i.e., when, tomato puree is mixed to a large excess of oil), the diffusion reached a plateau and after 30 min, only 5 to 7% of lycopene of fresh tomato reached the oil phase (Page et al., 2012). Recent studies in carrots and tomatoes indicated that tissue disruption and especially the plant cell wall or the integrity of plastid containing carotenoid cells is a major factor limiting the diffusion (Palmero et al., 2013). This partially explains that cooked products, where tissues are disrupted by the process, exhibit a better bioaccessibility for their carotenoids. However, our researches indicated that the processing methods (hot- or cold-break) deeply affect the diffusivity of the lycopene of tomato purees (Page et al., 2012), and we hypothesized that biochemical transformation of plastids, in addition to tissue disruption may explain this differences, and that the very initial heating step during their processing is a crucial step for enhancing the lycopene release from tomato.
In this study, we set up an experimental design in order to measure the temperature and duration limits that trigger the difference of diffusivity observed in hot-break purees. Tomato was treated at growing temperatures and during growing duration before or after their grinding as occurred in hot- or cold-break methods respectively.
Our results confirmed that the very initial heating step before tissue disruption is the critical point that modify lycopene diffusivity, and the minimal temperature necessary to trigger the effect was around 60-70°C. We hypothesized from these parameters that the enhancement of lycopene release may result of phenomena differing from cell-wall disruption.