Anti-fungal activity and preliminary active components separation from ethanol extracts in Saffron (Crocus sativus L.) lateral buds

Highlights

• Saffron lateral buds were non-medicine part for traditional medicine plant of Crocus sativus L.

• The discarded saffron lateral buds contains several bioactive compounds.

• Saffron lateral bud ethanol extracts showed excellent antifungal capacities.

• The antifungal effects are stable in neutral and acidic pH ranges.

• Saffron lateral buds were potential underutilized natural preservative resources.

Abstract

Saffron (Crocus sativus L.) is renowned for the active compounds contained in its stigmas, which are used in traditional medicine and as a spice. However, although the stigmas are well above the average yield, the lateral buds of saffron are usually discarded in saffron culturing. In order to expand saffron resource utilization, this study assessed the anti-fungal activities of saffron lateral bud ethanol extracts on six common food-borne pathogenic fungi, as well as investigated the stability of these activities under various heat and pH conditions. Furthermore, the active anti-fungal components of ethyl acetate phase were preliminarily separated by silica gel column chromatography technology and its major chemical constituents were investigated by HPLC-MS/MS. Results revealed that the ethyl acetate phase of saffron lateral bud ethanol extracts elicited a remarkable anti-fungal effect against the tested fungi, especially Aspergillus niger (83.47 %) and Trichoderma viride (79.93 %). Moreover, these inhibitory effects were stable in neutral and acidic pH ranges at temperatures < 100 °C. The ethyl acetate phase can further be separated into eight fractions by silica gel column chromatography, of which fraction 6 (F6) had the strongest anti-fungal effect by anti-fungal activity evaluation in vitro. HPLC-MS/MS analysis showed that the major compounds of F6 mostly belonged to polyphenols. To summarize, these findings demonstrated that saffron lateral buds are a potentially efficient and affordable source of natural preservatives for use in food.

Introduction

Microbial activities are the primary mode by which many foods spoil and are often responsible for the loss of quality and safety (Mead et al., 1999; McCabe-Sellers and Samuel, 2004). Food deterioration results in food loss and decreases its edible value, thereby incurring significant economic losses in the commercialization phase and poses the risk of food poisoning (Creppy, 2002; Lv et al., 2020; Sengun et al., 2008). According to estimates in China, 20–30 % of food is lost to spoilage each year (Mahmoud, 2019; Ritota and Manzi, 2020). In order to prolong the shelf life of food and keep food fresh, the addition of preservatives is necessary, of which chemical preservatives are extensively used (Abdulmumeen et al., 2012; Messager et al., 2004). However, researchers have found that some chemical preservatives pose serious consequences, including cancer, deformity, and bromatoxism. Thus, finding efficient, safe, steady, and broad-spectrum food preservatives has become imperative to avoid the side effects of chemical preservatives (Hsueh et al., 2005; Lai et al., 2002; Pitten et al., 2003). Natural food preservatives, in accordance with the aforementioned issues (Ben et al., 2007; Carocho et al., 2015), possess promising natural antimicrobial agents with potential applications in the food industry that could control pathogenic microbes. Many plant extracts have recently increased in popularity and are of scientific interest due to their antibacterial and anti-fungal activities (Granato et al., 2017; Fierascu et al., 2018; Tajkarimi et al., 2010). Previous studies have reported the antimicrobial properties of plant extracts containing phenols (Jurd et al., 1971; King et al., 1972; Rawat et al., 2018), alkaloids (Adewole et al., 1994; Nissanka et al., 2001; Yan et al., 2007), flavonoids (Lu et al., 2002; Pistelli and Giorgi, 2012; Sharma and Bharat, 2016), anthraquinone (Kosalec et al., 2013; Locatelli et al., 2011; Wu et al., 2006), coumarin (Arshad et al., 2011; Govori et al., 2010), and saponins (Avato et al., 2006; Elekofehint et al., 2019), among others.

Saffron (Crocus sativus L.) is a flowering plant that belongs to the Iridaceae family (Khazdair et al., 2015), which is produced by dring the long orange-red stigmas of the saffron crocus (Aytekin and Acikgoz, 2008). It is one of the most costly traditional medicine plant products and is sold for 200–1600 USD/kg in the world markets, depending on the quality (Gresta et al., 2009; José Bagur et al., 2017; Sampathu et al., 1984). Pharmacological studies and clinical practices have demonstrated that saffron stigmas contain many active compounds that possess promising biological functions, including its effects on blood circulation, as a sedative analgesic, anticonvulsant, antidepressant, anxiolytic, hypolipidemic, anti-atherogenic, anti-hypertensive, antidiabetic, and anti-cancer properties, among others (Christodoulou et al., 2019; Fernández-Albarral et al., 2020; Ghaffari and Roshanravan, 2019; Hosseini et al., 2018; Kianbakht and Hajiaghaee, 2011; Ríos et al., 2015). Furthermore, the saffron stigma is used as a spice and condiment for food, as well as a dye for thousands of years (Basker and Negbi, 1983; Fernández-Albarral et al., 2020). Due to its potential market prospects, many countries are devoted to saffron production. Saffron is mainly cultivated in the European Mediterranean region and Asia, with Iran as the primary producer (85 %) (Ghaffari and Roshanravan, 2019; Milajerdi and Mahmoudi, 2014).

In China, there are two main steps when cultivating saffron in terms of climate. First, plants flower indoors, and their stigmas are harvested, then plants are cultivated in the field so that daughter corms may form. To obtain higher quantity and quality saffron, their lateral buds must be discarded, which is based on the size of the maternal corms, including one bud (maternal corms < 16 g), two buds (16–25 g), and three buds (> 25 g). Although these products are well above the average stigma yield, saffron lateral buds are usually discarded in saffron culturing. Previous studies have shown that the lateral bud contains several bioactive compounds, including alkaloids, phenolic compounds, kaempferols, and anthraquinone (Serrano-Díaz et al., 2012), which have considerable developmental and utilization value. However, very little research has focused on lateral bud utilization. In this study, discarded saffron lateral buds were used as raw materials, and the anti-fungal activities of the ethanol extracts on six common food-borne pathogenic fungi were assessed. The stability of this activity under various heat and pH conditions was also investigated. Furthermore, the active anti-fungal components were preliminarily separated by silica gel column chromatography technology and high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The results obtained will provide basic data and technical support for the utilization of saffron resources, as well as supply a potentially efficient and affordable source of natural preservatives for use in food.