Basil essential oil product formulation by paste encapsulation method for reducing pre- and post-harvest losses of mango

Abstract

Ocimum spp., or ‘basils,’ is one of the most significant genera in Lamiaceae, the richest essential oil-producing plant family. Its essential oils comprise phenylpropanoids like estragole, eugenol and methyl eugenol, monoterpenes like geranial, neral and α-ocimene and sesquiterpenes like β-caryophyllene, α-cubebene and γ-muurolene. In agriculture, phenylpropanoids, particularly methyl eugenol, are utilised. The compound has the capacity to attract oriental fruit flies (Bactrocera dorsalis), the most destructive pest of tropical fruits. Additionally, the essential oils from this genus of plants are antimicrobial agents that control plant pathogens. The ‘Nam Dok Mai Si Thong’ mango has been globally exported as it is one of the most popular tropical fruits. It is well-liked due to its sweet taste and attractive appearance. During the mango production, infestation of B. dorsalis, a tropical fruit pest, and infection of Colletotrichum spp., the post-harvest fungus that causes mango anthracnose, hinder domestic and worldwide markets. Chemical pesticides are the main treatment for the infestations. However, environmental and health considerations limit their use. Essential oils from basils possess antifungal properties, particularly against fungi that cause post-harvest mango disease. Nonetheless, essential oil-utilising under environmental circumstances may limit its use in horticulture as temperature, light, and oxygen are uncontrollable. Encapsulation preserves bioactive, volatile and quickly degradable compounds from biochemical and thermal breakdown. Among the various methods to encapsulate, paste encapsulation is the simplest and most affordable method of encapsulating. Through chemical and mechanical interactions between the core and wall components, essential oil is encapsulated. This thesis evaluated the efficacy of the essential oils from basils in the management of ‘Nam Dok Mai Si Thong’ mango defects and developed products utilising low-cost, innovative technologies. The first study determined the chemical compositions of essential oils from the commercially available Thai Ocimum species and investigated their effectiveness as oriental fruit fly attractants. All basils, viz., red and white holy basils, Thai basil, lemon basil and tree basil, contained methyl eugenol. Red and white holy basil essential oils attracted male oriental fruit flies at a similar rate (~25%) to the commercial fruit fly attractant. White holly basil oil was paste-encapsulated with maltodextrin (MD) and gum arabic (GA) to control active component release. Numerous porous structures discovered by scanning electron microscopy demonstrated that the MD:GA (25:75) combination had the highest oil loading efficiency (9.40%). Traces of essential oil functional groups in the encapsulated polymer were confirmed by Fourier transform infrared spectra. In addition, the field investigation indicated that white holy basil encapsulated product improved the fruit fly attraction by preserving the essential oil release rate. Partial Least Squares (PLS) correlation models were used to assess which post-harvest characteristics were crucial for determining the ripening, disease infection and essential oil-induced damage. Physiochemical (%weight loss, peel colour, firmness, pH and peel electrolyte leakage) and biochemical (titratable acidity, total soluble solids, total phenolic compounds, total flavonoid compounds, antioxidants, total sugar and reducing sugar content) parameters were monitored and correlated with visual post-harvest physiological responses during storage. Lightness (L*) and b* value for non-destructive parameter, as well as pH and total soluble solids for destructive parameter, demonstrated the strongest connections with the mango ripening phase. Similar relationships were seen between the same markers and the severity of physical damage and mango post-harvest disease infection. Regarding the quality of the fruit, the Near Infrared Spectroscopy (NIR) absorbent data also described the biochemical changes in the water and enzymes. Thai basil (Ocimum basilicum var. thyrsiflora) oil and oil encapsulate vapour were tested for their ability to suppress Colletotrichum sp., the primary mango pathogen. The fungus was cultured on a PDA with oil vapour (50-1,500 µL/L air space) on a dual culture plate for an in vitro experiment. The ex vitro trial was conducted by keeping commercially mature mango fruit with the essential oil on cotton balls in a 1-litre perforated plastic container. Observations were made of the mango fruit’s weight loss and appearance (ripening-rotting, burning and discolouration indices). The in vitro investigation revealed that Thai basil oil exhibited up to 50% inhibition of mycelium growth with 125 µL/L air space. In the ex vitro experiment, the lesser quantity of the oil (25 - 13 µL) was able to maintain acceptable mango characteristics. Therefore, Thai basil oil has the potential to be a natural antifungal agent for preserving the aesthetic quality of mangoes after harvest. Utilising the information gleaned from these tests, Thai basil oil was encapsulated using a previous encapsulation process with the most oil-capsulated formulation, a 25:75 MD:GA ratio. Mango was wounded on the skin prior to inoculation with the confirmed Colletotrichum strain mycelium plug on the wound and then placed in a 1-litre plastic container alone and together with 25 µL of Thai basil essential oil on the cotton ball, 2 g of essential oil-encapsulated powder, and essential oil plus encapsulated essential oil. The samples were then kept for four days in a temperature- and humidity-controlled environment at 17–19 °C and 75–85% RH, respectively. The outcome revealed that Thai basil essential oil on the cotton ball and Thai basil oil enclosed in a capsule could maintain the quality of mangoes. With mycelium plug infection, they could not maintain mango quality and prevent the spread of the disease. These studies demonstrate that white holy basil oil can attract oriental fruit flies and that paste encapsulation can maintain the oil’s effectiveness in the environment. Thai basil oil also suppresses the mycelium growth of the mango anthracnose fungus. Nonetheless, essential oil vapour can cause skin burning and deterioration of cell compartments, thereby promoting fungal infection. However, it is intriguing to use Thai basil oil properly. Employing an encapsulated natural material to control ‘Nam Dok Mai Si Thong’ mango fruit defects may minimise the usage of hazardous pesticides. Additionally, it improves horticultural crops, namely basils. The agronomic effort is still required to generate high-quality essential oil raw materials for practical use.