Effect of Thymol and Carvacrol Encapsulated in Hp‐Β‐Cyclodextrin by Two Inclusion Methods against Geotrichum citri‐aurantii

Abstract

Geotrichum citri‐aurantii causes sour rot in citrus fruits and is responsible for important economic losses during storage. However, the availability of chemical fungicides for the control of this pathogen is limited. Thus, the aim of this research was to evaluate the antifungal efficacy of thymol and carvacrol encapsulated in 2‐hydroxylpropyl‐beta‐cyclodextrin (HP‐β‐CD) (prepared by the microwave irradiation method [MW] and solubility method [S]) for inhibition of G. citri‐aurantii using in vitro bioassays broth (micro and macrodilutions methods) and inoculated food testing. Both encapsulated thymol and carvacrol were shown to be effective for inhibiting G. citri‐aurantii growth in in vitro assays. Thymol was more effective in inhibiting G. citri‐aurantii, while better encapsulation was provided by MW. HP‐β‐CD‐thymol encapsulated by MW (HP‐β‐CD‐thymol‐MW) showed the lowest 50% effective dose (ED50 = 1.16 mM), minimum inhibitory concentration (MIC = 5.06 mM), and minimum fungicide concentration (MFC = 52.6 mM). HP‐β‐CD‐thymol‐MW was found highly effective in reducing the growth rate and mycelial growth inhibition. Finally, HP‐β‐CD‐thymol‐MW and HP‐β‐CD‐carvacrol‐MW showed a higher persistent effect than thymol and carvacrol in their natural form in inhibiting this fungus. Therefore, HP‐β‐CD‐thymol‐MW could be a promising alternative to synthetic fungicides for controlling G. citri‐aurantii, the causal agent of citrus sour rot. Practical Application Encapsulated thymol and carvacrol in HP‐β‐Cyclodextrins are effective for controlling G. citri‐aurantii in in vitro experiments. Encapsulation of thymol and carvacrol by microwave irradiation method (MW) was more effective than the solubility (S) method. Thymol was more effective than carvacrol, and the best results on G. citri‐auriantii inhibition were achieved using the HP‐β‐CD‐thymol‐MW method (which gave the lowest ED50, MIC, and MFC).

Thymol Encapsulated into HP-β-Cyclodextrin as an Alternative to Synthetic Fungicides to Induce Lemon Resistance against Sour Rot Decay

“…HP-β-CDs (CAS Number 128446-35-5), with an average degree of substitution of 0.5–1.3 units of 2-hydroxypropyl (C 3 H 7 O) for each glucose unit, were provided by AraChem (Tilburg, Holland). The complexation procedure of thymol in HP-β-CDs was fulfilled by using the microwave method (MW) and dehydrated by spray drying [ 22 ]. The entrapment efficiency (EE) of thymol complexes in HP-β-CDs was 82.8 ± 0.6. expressed as EE (g 100g −1 ) [ 22 ].…”

“…The complexation procedure of thymol in HP-β-CDs was fulfilled by using the microwave method (MW) and dehydrated by spray drying [ 22 ]. The entrapment efficiency (EE) of thymol complexes in HP-β-CDs was 82.8 ± 0.6. expressed as EE (g 100g −1 ) [ 22 ].…”

“…In this way, it is possible to reduce the negative effects of pure essential oils when they are applied directly on fruit surface and, in addition, their effectiveness against microorganisms is maintained. Recently, Serna-Escolano et al [ 22 ] and Rodríguez-López et al [ 23 ] have proposed the use of essential oils like carvacrol and thymol encapsulated in HP-β-CD to control the in vitro growth of molds and bacteria, respectively. In both papers, we found that the microwave encapsulation method (HP-β-CD-thymol-MW) was the best to encapsulate the essential oils and to control G. citri-aurantii growth and its sporulation and bacteria growth.…”

“…In both papers, we found that the microwave encapsulation method (HP-β-CD-thymol-MW) was the best to encapsulate the essential oils and to control G. citri-aurantii growth and its sporulation and bacteria growth. Additionally, Serna-Escolano et al [ 22 ] evaluated the in vitro effect of carvacrol and thymol on G. citri-aurantii and 5.06 and 52.6 mM were obtained as minimum inhibitory concentration (MIC) and minimum fungicide concentration (MFC), respectively.…”

“…The curative action consists in the ability of the fungicide to limit the development of the pathogen inside the tissues, when applied in the latent period, that is, in the interval between the penetration and the appearance of the first symptoms. For this purpose, 50 and 25 mM HP-β-CD-thymol complex concentrations were used, which were close to the minimal fungicidal concentration (MFC) and half of the MFC established in our previous study [ 22 ].…”