L. E. B. Soledade

Phenolic profile, antioxidant activity and palynological analysis of stingless bee honey from Amazonas, Northern Brazil

In this study honey samples produced by Melipona (Michmelia) seminigra merrillae, collected in seven counties distributed in the central and southern region of Amazonas state in Brazil, were analysed for their botanical origin, content and profile of phenolic compounds, and antioxidant and antimicrobial activities. Twenty-two pollen types were identified. The total phenolic content ranged from 17 to 66 mg GAE/g of extract; the highest contents were found in honeys produced from pollen types such as Clidemia and Myrcia. The antioxidant activity was higher in the samples that contained higher quantities of phenolic compounds. In relation to the antibacterial activity, samples CAD3, CAD4 and SAD3 presented the best results. Fourteen phenolic compounds were determined. Among them, we identified the flavonoid taxifolin, which has not previously been described in honeys from stingless bees, and we report the identification of catechol in Brazilian honey samples for the first time.

Rosemary (Rosmarinus officinalis L.) extract

The restriction to the use of synthetic antioxidants has fostered the research on natural antioxidants, taking into account that the prolonged usage of these substances can harm seriously the human being provoking degenerative diseases. In the present study, the antioxidant effect of the ethanolic rosemary (Rosmarinus officinalis L.) extract on the oxidative stability of edible vegetable oils was investigated by means of the pressurized differential scanning calorimetry (PDSC) and oven test techniques. The rosemary extract, at the concentration of 2,000xa0mgxa0kg−1, as well as the synthetic antioxidant tert-butylhydroquinone (TBHQ) at the concentrations of 100 and 200xa0mgxa0kg−1 were added to samples of sunflower oil, corn oil, and soybean oil. The fatty acid profiles of the vegetable oils were determined by gas chromatography–mass spectrometry confirming the elevated contents of unsaturated fatty acids. The thermogravimetric analysis showed that the rosemary extract is stable at the frying temperature of the oils. The results of the oxidative stability demonstrated that the extract of Rosmarinus officinalis displayed a more effective protective action in the PDSC technique, when compared with the synthetic antioxidant TBHQ, indicating that it is a promising source of natural antioxidants for edible vegetable oils.

Rancimat and PDSC accelerated techniques for evaluation of oxidative stability of soybean oil with plant extracts

Taking into account the importance of natural antioxidants in the preservation of oils and fats, the present study evaluated the antioxidant action of five plant extracts in the control of soybean oil stability, by means of the accelerated techniques Rancimat and PDSC. These plants are rosemary (Rosmarinus officinalis L.), chamomile (Matricaria recutita L.), coriander (Coriandrum sativum L.), fennel (Foeniculum vulgare), and senna (Cassia angustifolia Vahl). The plant extracts and also the synthetic antioxidant BHT were added to the samples of crude soybean oil at the concentration of 1,000xa0mgxa0kg−1. The values of total phenolic contents ranged from 8.7xa0±xa00.4 to 63.0xa0±xa02.3xa0mgxa0GAExa0g−1 extract and a strong positive correlation was observed between the total phenolic contents and the overall antioxidant activity of the plant extracts. Such high values indicate a good protection of the analyzed soybean oil, moreover for the Rosemary extract that was superior to the remaining extracts. In the Rancimat technique the rosemary extract was more effective than the synthetic BHT antioxidant. The OIT values of Rosemary extract and the BHT antioxidant were equivalent, and the former, showed the highest phenolic contents among the extracts, for all the performed tests, confirming that it is a powerful natural source of antioxidants.

Ethanolic extracts of Moringa oleifera Lam.

This paper reports the evaluation of the antioxidant potential of the ethanolic extracts of the leaves (EL), flowers (EF), seed pods (EP) and seeds (ES) from Moringa oleifera Lam. The antioxidant potential was assessed, upon the addition of the extracts to fish oil, by means of the total extractable phenol content (TEP), the DPPH· free radical scavenging efficiency and using pressurized differential scanning calorimetry (P-DSC). The results of TEP and DPPH· showed that the ES extract does not present a potential to be used as an antioxidant additive, and it was thus discarded from the remaining analyses. Thus, the following treatments were prepared: pure fish oil, fish oil with BHT (100xa0mgxa0kg−1), fish oil with TBHQ (100xa0mgxa0kg−1) and fish oil with EL, EF and EP—all at the concentration of 100xa0mgxa0kg−1, in relation to the total extractable phenolics contained in each one of the extracts. The leaf and flower extracts displayed a protecting effect, with an increase in about 20 and 11xa0% of the OIT values, respectively. However, such protection was smaller than that conferred by the synthetic antioxidants utilized. As for the thermal analysis results, it was noticed that EL presented the highest thermal stability among the extracts.

Thermal degradation of honeys and evaluation of physicochemical properties

The physicochemical characterization and thermal profile of honeys produced by stingless bees are poorly known, mainly due to the high diversity of flora mellifera and to the low production that is inherent of these species. The objective of this study was to determine the physicochemical characteristics of five samples of honey from bees from the species Melipona seminigra merrillae of Amazonas State, Brazil. The thermal degradation profile of these honey samples was evaluated by thermogravimetry in order to contribute with the establishment of a quality standard of honeys produced from Brazilian stingless bees. Thus, the following analyses were performed: reducing sugars, moisture, hydroxymethylfurfural, protein, ash, pH, and acidity. The results showed that the current legislation concerning the honey of Apis mellifera is not an appropriate standard for all the properties analyzed, reinforcing the need for a honey standard including the honeys of all Brazilian bees. The honey samples displayed similar thermal degradation profiles, with the thermal process starting at room temperature and ending at a temperature next to 600xa0°C.